JEE 3D Geometry PYQs
JEE 3D Geometry PYQs are an important part of the JEE Mathematics syllabus. They help you understand the kind of questions asked from this chapter and show how well you know the main concepts, such as direction cosines, direction ratios, distance formula, section formula, lines in space, planes, angle between lines, and shortest distance.
In the exam, 3D geometry questions usually come as direct numerical problems or simple concept-based questions. The good thing is that this chapter becomes much easier when your basics are clear. Once you understand the concepts properly and know which formula or method to use, solving questions feels much more manageable. You do not need to think of 3D geometry as a very difficult chapter. With regular revision and smart practice, it can become one of the more scoring parts of JEE Mathematics.
In this blog, you will find a simple formula PDF, a section for important JEE 3D Geometry PYQs in download format, a few practice questions with answers, and some extra questions to solve on your own. You will also learn about common mistakes students often make and a few easy tips to save time in the exam.
JEE 3D Geometry Important PYQs PDF
This PDF can include the most important previous year questions from 3D geometry. It may cover topics like coordinates of a point in space, distance between two points, section formula, direction cosines, direction ratios, equation of a line, equation of a plane, angle between two lines, angle between planes, and shortest distance.
Practicing these questions will help you understand the exam pattern better. It will also improve your speed, accuracy, and confidence before the exam.
Important Formulas for JEE 3D Geometry PYQs
You only need a few important formulas and ideas to solve most 3D geometry questions in JEE. These formulas help you understand points, lines, planes, distances, and angle-based problems more clearly.
You can download the full formula PDF from the link above. Here is a quick look at some of the main formulas:
Concept | Formula |
Distance Between Two Points | √[(x₂ − x₁)² + (y₂ − y₁)² + (z₂ − z₁)²] |
Section Formula | ((mx₂ + nx₁)/(m + n), (my₂ + ny₁)/(m + n), (mz₂ + nz₁)/(m + n)) |
Direction Cosines Relation | l² + m² + n² = 1 |
Line in Symmetric Form | (x − x₁)/a = (y − y₁)/b = (z − z₁)/c |
Equation of Plane | ax + by + cz + d = 0 |
Angle Between Two Lines | cos θ = (a₁a₂ + b₁b₂ + c₁c₂) / [√(a₁²+b₁²+c₁²) √(a₂²+b₂²+c₂²)] |
Angle Between Two Planes | cos θ = (a₁a₂ + b₁b₂ + c₁c₂) / [√(a₁²+b₁²+c₁²) √(a₂²+b₂²+c₂²)] |
Distance of Point from Plane | |ax₁ + by₁ + cz₁ + d| / √(a² + b² + c²) |
Condition for Perpendicular Planes | a₁a₂ + b₁b₂ + c₁c₂ = 0 |
Condition for Parallel Planes | a₁/a₂ = b₁/b₂ = c₁/c₂ |
Direction Ratios to Direction Cosines | l = a/√(a²+b²+c²), m = b/√(a²+b²+c²), n = c/√(a²+b²+c²) |
These formulas are commonly used in questions based on points, lines, planes, direction ratios, direction cosines, angles, and distances in space. If you revise them properly, many JEE questions start to feel much easier.
Top 5 Common Mistakes to Avoid in JEE 3D Geometry PYQs
Many students find 3D geometry confusing at first because it has many formulas and also needs good visual understanding. But most mistakes happen because small details are missed while solving. Here are some common mistakes you should avoid:
Mixing up direction ratios and direction cosines
Direction ratios and direction cosines are related, but they are not the same. Students often use them in the same way without converting properly when needed.
Making sign mistakes in the 3D distance formula
A small sign mistake while subtracting coordinates can change the whole answer. This happens often in distance and section formula questions.
Using the wrong formula for angle between lines and planes
The formulas for angle between lines and angle between planes look very similar, so students often confuse where and how to use them.
Forgetting the modulus in the distance of a point from a plane
The distance of a point from a plane is always positive. Many students forget the modulus sign and end up getting a negative answer.
Not visualising the geometry properly
3D geometry is not only about formulas. You also need to understand how points, lines, and planes are placed in space. If you solve in a hurry without visualising, mistakes become more likely.
List of JEE 3D Geometry PYQs
Here is a short set of JEE-style 3D geometry questions for practice. These include common question types from distance, direction cosines, lines, planes, and angles. Solving them regularly can help you become faster and more confident.
Question 1
Let the line $$L_{1}$$ be parallel to the vector $$-3\widehat{i} +2\widehat{j} + 4\widehat{k}$$ and pass through the point (2, 6, 7), and the line $$L_{2}$$ be parallel to the vector $$2\widehat{i} +\widehat{j} + 3\widehat{k}$$ and pass through the point (4, 3, 5). If the line $$L_{3}$$ is parallel to the vector $$-3\widehat{i} +5\widehat{j} + 16\widehat{k}$$ and intersects the lines $$L_{1}$$ and $$L_{2}$$ at the points C and D, respectively, then $$|\overrightarrow{CD}|^2$$ is equal to :
correct answer:- 1
Question 2
For a triangle ABC, let $$\overrightarrow{p} = \overrightarrow{BC}, \overrightarrow{q}= \overrightarrow{CA}$$ and $$\overrightarrow{r} = \overrightarrow{BA}$$. If $$|\overrightarrow{p}| = 2\sqrt{3}, |\overrightarrow{q}|=2$$ and $$\cos\theta = \frac{1}{\sqrt{3}}$$ where $$\theta$$ is the angle between $$\overrightarrow{p}$$ and $$\overrightarrow{q}$$, then $$|\overrightarrow{p} \times \left(\overrightarrow{q}-\overrightarrow{3r}\right)|^2 +3|\overrightarrow{r}|^2$$ is equal to :
correct answer:- 4
Question 3
Let the line L pass through the point ( - 3, 5, 2) and make equal angles with the positive coordinate axes. If the distance of L from the point ( - 2, r, 1) is $$\sqrt{\frac{14}{3}}$$, then the sum of all possible values of r is:
correct answer:- 1
Question 4
Let L be the line $$\frac{x+1}{2}=\frac{y+1}{3}=\frac{z+3}{6}$$ and let S be the set of all points (a, b, c) on L, whose distance from the line $$\frac{x+1}{2}=\frac{y+1}{3}=\frac{z-9}{0}$$a long the line L is 7. Then $$\sum_{(a,b,c)\in S} (a+b+c) $$ is equal to :
correct answer:- 4
Question 5
Let a vector $$\vec{a} = \sqrt{2}\,\hat{i} - \hat{j} + \lambda \hat{k}, \quad \lambda > 0,$$ make an obtuse angle with the vector $$\vec{b} = -\lambda^{2}\hat{i} + 4\sqrt{2}\,\hat{j} + 4\sqrt{2}\,\hat{k}$$ and an angle $$\theta, \dfrac{\pi}{6} < \theta < \dfrac{\pi}{2}$$, with the positive z-axis. If the set of all possible values of $$\lambda$$ is $$( \alpha, \beta) - \{\gamma\}$$, then $$\alpha + \beta + \gamma$$ is equal to __________.
correct answer:- 5
Question 6
The vertices B and C of a triangle ABC lie on the line $$\frac{x}{1}=\frac{1-y}{-2}=\frac{z-2}{3}$$ The coordinates of A and B are (1, 6, 3) and (4, 9, $$\alpha$$) respectively and C is at a distance of 10 units from B. The area (in sq. units) of $$\triangle$$ABC is :
correct answer:- 1
Question 7
Let the direction cosines of two lines satisfy the equations : 4l + m - n =0 and 2mn + l0nl +3lm= 0. Then the cosine of the acute angle between these lines is :
correct answer:- 3
Question 8
If the image of the point $$P(1 , 2, a)$$ in the line $$ \frac{x-6}{3} = \frac{y - 7}{2} = \frac{7 -z}{2}$$ is $$Q(5, b, c)$$, then $$ a^{2}+b^{2}+c^{2}$$ is equal to
correct answer:- 2
Question 9
Let $$ P(\alpha,\beta, \gamma)$$ be the point on the line $$\frac{x-1}{2}=\frac{y+1}{-3}=z$$ at a distance $$4\sqrt{14}$$ from the point (1, -1, 0) and nearer to the origin. Then the shortest di stance, between the Lines $$\frac{x-\alpha}{1}=\frac{y-\beta}{2}=\frac{z-\gamma}{3}$$ and $$\frac{x+5}{2}= \frac{y-10}{1}=\frac{z-3}{1}$$, is equal to
correct answer:- 2
Question 10
Let the lines $$L_{1}:\overrightarrow{r}=\widehat{i}+2\widehat{j}+3\widehat{k}+\lambda(2\widehat{i}+3\widehat{j}+4\widehat{k}),\lambda \in \mathbb{R}$$ and $$L_{2}:\overrightarrow{r}=(4\widehat{i}+\widehat{j})+\mu (5\widehat{i}+2\widehat{j}+\widehat{k}),\mu \in \mathbb{R}$$, interest at the point R. Let P and Q be the points lying on lines $$L_{1}$$ and $$L_{2}$$ respectively, such that $$|\overrightarrow{PR}|=\sqrt{29}$$ and $$|\overrightarrow{PQ}|=\sqrt{\frac{47}{3}}$$. If the point P lies in the first octant, then $$27(QR)^{2}$$ is equal to
correct answer:- 3
Question 11
Let a line L passing through the point P (1, 1, 1) be perpendicular to the lines $$\frac{x-4}{4}=\frac{y-1}{1}=\frac{z-1}{1}$$ and $$\frac{x-17}{1}=\frac{y-71}{1}=\frac{z}{0}$$. Let the line L intersect the yz-plane at the point Q. Another line parallel to L and passing through the point S (1, 0, - 1) intersects the yz-plane at the point R. Then the square of the area of the parallelogram PQRS is equal to ___.
correct answer:- 6
Question 12
The sum of all values of $$\alpha$$, for which the sho1test distance between the lines
$$\frac{x+1}{\alpha}=\frac{y-2}{-1}=\frac{z-4}{-\alpha}$$ and $$\frac{x}{\alpha}=\frac{y-1}{2}=\frac{z-1}{2\alpha}$$ is $$\sqrt{2}$$, is
correct answer:- 4
Question 13
If the distances of the point (1 , 2, a) from the line $$\frac{x-1}{1}=\frac{y}{2}=\frac{z-1}{1}$$ along the lines $$L_{1}:\frac{x-1}{3}=\frac{y-2}{4}=\frac{z-a}{b}$$ and $$L_{2}:\frac{x-1}{1}=\frac{y-2}{4}=\frac{z-a}{c}$$ are equal, then a + b + c is equal to
correct answer:- 1
Question 14
If the image of the point $$P(a, 2, a)$$ in the line $$\frac{x}{2}=\frac{y+a}{1}=\frac{z}{1}$$ is Q and the image of Q in the line $$\frac{x-2b}{2}=\frac{y-a}{1}=\frac{z+2b}{-5}$$ is P, then a + b is equal to _____.
correct answer:- 3
Question 15
Let P be a point in the plane of the vectors $$ \overrightarrow{AB}=3\widehat{i} + \widehat{j}-\widehat{k} \text{ and }\overrightarrow{AC}=\widehat{i}-\widehat{j}+3\widehat{k}$$ such that P is equidistant from the Lines AB and AC. If $$ \mid \overrightarrow{AP} \mid=\frac{\sqrt{5}}{2} $$ then the area of the triangle ABP is:
correct answer:- 1
Question 16
If the distance of the point $$P(43, \alpha, \beta), \beta<0,$$ from the line $$\overrightarrow{r} = 4\widehat{i}-\widehat{k}+\mu(2\widehat{i}+3\widehat{k}), \mu \in \mathbb{R}$$ along a line with direction ratios 3, -1, 0 is $$13\sqrt{10},$$ then $$ \alpha ^{2}+ \beta^{2}$$ is equal to______
correct answer:- 170
Question 17
Let a line pass through two distinct points P(−2,−1, 3) and , and be parallel to the vector $$3\widehat{i}+2\widehat{j}+2\widehat{k}$$. If the distance of the point Q from the point R(1, 3, 3) is 5 , then the square of the area of △PQR is equal to :
correct answer:- 2
Question 18
The perpendicular distance, of the line $$\frac{x-1}{2}=\frac{y+2}{-1}=\frac{z+3}{2}$$ from the point P(2,−10, 1), is :
correct answer:- 4
Question 19
Let $$ L_1: \frac{x-1}{2}=\frac{y-2}{3}=\frac{z-3}{4} \text{ and } L_2: \frac{x-2}{3}=\frac{y-4}{4}=\frac{z-5}{5} $$ be two lines. Then which of the following points lies on the line of the shortest distance between $$L_1 \text{ and } L_2 $$ ?
correct answer:- 1
Question 20
Let $$L_1:\frac{x-1}{3}=\frac{y-1}{-1}=\frac{z+1}{0}$$ and $$L_2:\frac{x-2}{2}=\frac{y}{0}=\frac{z+4}{\alpha}$$, $$\alpha \in R$$, be two lines, which intersect at the point $$B$$. If $$P$$ is the foot of perpendicular from the point $$A(1,1,-1)$$ on $$L_2$$, then the value of $$26\alpha(PB)^{2}$$ is ______
correct answer:- 216
Question 21
The distance of the line $$\frac{x-2}{2}=\frac{y-6}{3}=\frac{z-3}{4}$$ from the point (1, 4, 0) along the line $$\frac{x}{1}=\frac{y-2}{2}=\frac{z+3}{3}$$ is :
correct answer:- 3
Question 22
If the square of the shortest distance between the lines $$frac{x-2}{1}=\frac{y-1}{2}=\frac{z+3}{-3}$$ and $$\frac{x+1}{2}=\frac{y+3}{4}=\frac{x+5}{-5}\text{ is }\frac{m}{n}$$, where m, n are coprime numbers, then m + n is equals to:
correct answer:- 2
Question 23
Let the point A divide the line segment joining the points P(−1,−1, 2) and Q(5, 5, 10) internally in the ratio $$r : 1 (r > 0)$$. If O is the origin and $$(\overrightarrow{OQ}.\overrightarrow{OA})-\frac{1}{5}|\overrightarrow{OP}.\overrightarrow{OA}|^{2}=10$$. then the value of r is :
correct answer:- 4
Question 24
Let in a $$\triangle ABC$$, the length of the side $$AC$$ be $$6$$, the vertex $$B$$ be $$(1, 2, 3)$$ and the vertices $$A, C$$ lie on the line $$ \frac{x - 6}{3} = \frac{y - 7}{2} = \frac{z - 7}{-2}. $$ Then the area (in sq. units) of $$\triangle ABC$$ is:
correct answer:- 2
Question 25
Let the line passing through the points $$(-1,2,1)$$ and parallel to the line $$\frac{x-1}{2}=\frac{y+1}{3}=\frac{z}{4}$$ intersect the line $$\frac{x+2}{3}=\frac{y-3}{2}=\frac{z-4}{1}$$ at the point $$P.$$ Then the distance of $$P$$ from the point $$Q(4,-5,1)$$ is:
correct answer:- 2
Question 26
Let $$P$$ be the image of the point $$Q(7,-2,5)$$ in the line $$L:\;\frac{x-1}{2}=\frac{y+1}{3}=\frac{z}{4},$$ and $$R(5,p,q)$$ be a point on $$L.$$ Then the square of the area of $$\triangle PQR$$ is $$\underline{\hspace{2cm}}.$$
correct answer:- 957
Question 27
If the image of the point (4,4,3)in the line $$\frac{x-1}{2}=\frac{y-2}{1}=\frac{z-1}{3}$$ is $$(\alpha ,\beta ,\gamma)$$, then $$\alpha +\beta +\gamma$$ is equal to
correct answer:- 1
Question 28
Let $$A(x,y,Z)$$ be a point in $$xy-plain$$,which is equidistant from three points (0, 3, 2), (2, 0, 3) and (0, 0, 1). Let B = (1, 4, −1) and C = (2, 0, −2). Then among the statements $$(SI): \triangle ABC$$ is an isosceles right angled triangle, and (SI):the area of $$\triangle ABC$$ is $$\frac{9\sqrt{2}}{2}$$,
correct answer:- 3
Question 29
Let $$L_{1}: \frac{x-1}{1}=\frac{y-2}{-1}=\frac{z-1}{2}$$ and $$L_{2}: \frac{x+1}{-1}=\frac{y-2}{2}=\frac{z}{1}$$ be two lines. Let $$L_{3}$$ be a line passing through the point $$(\alpha ,\beta ,\gamma)$$ and be perpendicular to both $$L_{1}$$ and $$L_{2}$$. If $$L_{3}$$ intersects $$L_{1}$$, then $$|5\alpha -11\beta -8\gamma|$$ equals:
correct answer:- 3
Question 30
If the system of equations $$(\lambda-1)x+(\lambda-4)y+\lambda z=5 \\\lambda x+(\lambda-1)y+(\lambda-4)z=7 \\ (\lambda+1)x+(\lambda+2)y-(\lambda+2)z=9$$ has infinitely many solutions, then $$\lambda^{2}+\lambda$$ is equal to
correct answer:- 4
Question 31
Let a straight line L pass through the point P(2,-1,3) and be perpendicular to the lines $$\frac{x-1}{2}=\frac{y+1}{1}=\frac{z-3}{-2}$$ and $$\frac{x-3}{1}=\frac{y-2}{3}=\frac{z+2}{4}.$$ If the line L intersects the yz-plane at the point Q , then the distance between the points P and Q is :
correct answer:- 4
Question 32
Let the point, on the line passing through the points P(1, −2, 3) and Q(5, −4, 7), farther from the origin and at distance of 9 units from the point P, be $$(\alpha, \beta, \gamma)$$. Then $$\alpha^2 + \beta^2 + \gamma^2$$ is equal to:
correct answer:- 3
Question 33
If the shortest distance between the lines $$\frac{x+2}{2} = \frac{y+3}{3} = \frac{z-5}{4}$$ and $$\frac{x-3}{1} = \frac{y-2}{-3} = \frac{z+4}{2}$$ is $$\frac{38}{3\sqrt{5}}k$$, and $$\int_0^k [x^2]dx = \alpha - \sqrt{\alpha}$$, where [x] denotes the greatest integer function, then $$6\alpha^3$$ is equal to ______.
correct answer:- 48
Question 34
If the components of $$\overrightarrow{a} = \alpha \hat{i}+\beta \hat{j}+\gamma \hat{k}$$ along and perpendicular to $$\overrightarrow{b}= 3\hat{i}+\hat{j}-\hat{k}$$ respectively, are $$frac{16}{11}(3\hat{i}+\hat{j}-\hat{k})$$ and $$frac{1}{11}(-4\hat{i}-5\hat{j}-17\hat{k})$$, then $$\alpha^{2} + \beta^{2} + \gamma^{2}$$ is equals to :
correct answer:- 1
Question 35
The square of the distance of the point $$(\frac{15}{7},\frac{32}{7},7)$$ from the line $$\frac{x+1}{3}=\frac{y+3}{5}=\frac{z+5}{7}$$ in the direction of the vector $$\hat{i}+4\hat{j}+7\hat{k}$$ is :
correct answer:- 4
Question 36
If the system of equations $$\\2x + 3y - z = 5\\ x + \alpha y + 3z = -4\\ 3x - y + \beta z = 7\\$$ has infinitely many solutions, then $$13\alpha\beta$$ is equal to:
correct answer:- 2
Question 37
If the shortest distance between the lines $$\frac{x-\lambda}{-2} = \frac{y-2}{1} = \frac{z-1}{1}$$ and $$\frac{x-\sqrt{3}}{1} = \frac{y-1}{-2} = \frac{z-2}{1}$$ is $$1$$, then the sum of all possible values of $$\lambda$$ is:
correct answer:- 2
Question 38
Let the line of the shortest distance between the lines $$L_1: \vec{r} = (\hat{i} + 2\hat{j} + 3\hat{k}) + \lambda(\hat{i} - \hat{j} + \hat{k})$$ and $$L_2: \vec{r} = (4\hat{i} + 5\hat{j} + 6\hat{k}) + \mu(\hat{i} + \hat{j} - \hat{k})$$ intersect $$L_1$$ and $$L_2$$ at $$P$$ and $$Q$$ respectively. If $$(\alpha, \beta, \gamma)$$ is the midpoint of the line segment $$PQ$$, then $$2(\alpha + \beta + \gamma)$$ is equal to:
correct answer:- 21
Question 39
Let the system of equations $$x + 2y + 3z = 5$$, $$2x + 3y + z = 9$$, $$4x + 3y + \lambda z = \mu$$ have infinite number of solutions. Then $$\lambda + 2\mu$$ is equal to:
correct answer:- 2
Question 40
Consider a $$\triangle ABC$$ where $$A(1, 3, 2)$$, $$B(-2, 8, 0)$$ and $$C(3, 6, 7)$$. If the angle bisector of $$\angle BAC$$ meets the line BC at D, then the length of the projection of the vector $$\vec{AD}$$ on the vector $$\vec{AC}$$ is:
correct answer:- 1
Question 41
If the mirror image of the point $$P(3, 4, 9)$$ in the line $$\frac{x-1}{3} = \frac{y+1}{2} = \frac{z-2}{1}$$ is $$(\alpha, \beta, \gamma)$$, then $$14(\alpha + \beta + \gamma)$$ is:
correct answer:- 3
Question 42
Let P and Q be the points on the line $$\frac{x+3}{8} = \frac{y-4}{2} = \frac{z+1}{2}$$ which are at a distance of 6 units from the point $$R(1, 2, 3)$$. If the centroid of the triangle PQR is $$(\alpha, \beta, \gamma)$$, then $$\alpha^2 + \beta^2 + \gamma^2$$ is:
correct answer:- 3
Question 43
The distance, of the point $$(7, -2, 11)$$ from the line $$\frac{x-6}{1} = \frac{y-4}{0} = \frac{z-8}{3}$$ along the line $$\frac{x-5}{2} = \frac{y-1}{-3} = \frac{z-5}{6}$$, is :
correct answer:- 2
Question 44
If the shortest distance between the lines $$\frac{x-4}{1} = \frac{y+1}{2} = \frac{z}{-3}$$ and $$\frac{x-\lambda}{2} = \frac{y+1}{4} = \frac{z-2}{-5}$$ is $$\frac{6}{\sqrt{5}}$$, then the sum of all possible values of $$\lambda$$ is :
correct answer:- 2
Question 45
The position vectors of the vertices A, B and C of a triangle are $$2\hat{i} - 3\hat{j} + 3\hat{k}$$, $$2\hat{i} + 2\hat{j} + 3\hat{k}$$ and $$-\hat{i} + \hat{j} + 3\hat{k}$$ respectively. Let $$l$$ denotes the length of the angle bisector AD of $$\angle BAC$$ where D is on the line segment BC, then $$2l^2$$ equals :
correct answer:- 4
Question 46
Let the image of the point $$(1, 0, 7)$$ in the line $$\frac{x}{1} = \frac{y - 1}{2} = \frac{z - 2}{3}$$ be the point $$(\alpha, \beta, \gamma)$$. Then which one of the following points lies on the line passing through $$(\alpha, \beta, \gamma)$$ and making angles $$\frac{2\pi}{3}$$ and $$\frac{3\pi}{4}$$ with y-axis and z-axis respectively and an acute angle with x-axis?
correct answer:- 3
Question 47
The lines $$\frac{x-2}{2} = \frac{y}{-2} = \frac{z-7}{16}$$ and $$\frac{x+3}{4} = \frac{y+2}{3} = \frac{z+2}{1}$$ intersect at the point P. If the distance of P from the line $$\frac{x+1}{2} = \frac{y-1}{3} = \frac{z-1}{1}$$ is $$l$$, then $$14l^2$$ is equal to _____.
correct answer:- 108
Question 48
Let $$PQR$$ be a triangle with $$R(-1, 4, 2)$$. Suppose $$M(2, 1, 2)$$ is the mid point of $$PQ$$. The distance of the centroid of $$\Delta PQR$$ from the point of intersection of the line $$\frac{x-2}{0} = \frac{y}{2} = \frac{z+3}{-1}$$ and $$\frac{x-1}{1} = \frac{y+3}{-3} = \frac{z+1}{1}$$ is
correct answer:- 3
Question 49
A line with direction ratio $$2, 1, 2$$ meets the lines $$x = y + 2 = z$$ and $$x + 2 = 2y = 2z$$ respectively at the point $$P$$ and $$Q$$. If the length of the perpendicular from the point $$(1, 2, 12)$$ to the line $$PQ$$ is $$l$$, then $$l^2$$ is _______
correct answer:- 65
Question 50
Let $$O$$ be the origin, and $$M$$ and $$N$$ be the points on the lines $$\frac{x-5}{4} = \frac{y-4}{1} = \frac{z-5}{3}$$ and $$\frac{x+8}{12} = \frac{y+2}{5} = \frac{z+11}{9}$$ respectively such that $$MN$$ is the shortest distance between the given lines. Then $$\vec{OM} \cdot \vec{ON}$$ is equal to ______.
correct answer:- 9
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