Sign in
Please select an account to continue using cracku.in
↓ →
Join Our JEE Preparation Group
Prep with like-minded aspirants; Get access to free daily tests and study material.
Let $$z, w$$ be complex numbers such that $$\bar{z} + i\bar{w} = 0$$ and $$\arg zw = \pi$$. Then $$\arg z$$ equals
Given the first condition:
$$ \bar{z} + i\bar{w} = 0 $$
Isolate the conjugate of z:
$$ \bar{z} = -i\bar{w} $$
Take the complex conjugate on both sides of the equation, keeping in mind that the conjugate of a conjugate returns the original complex number, and the conjugate of $$ -i $$ is $$ i $$:
$$ z = i w $$
Multiply both sides of this equation by $$ -i $$ to express w in terms of z:
$$ -iz = -i(iw) $$
$$ -iz = w $$
$$ w = -iz $$
The second condition provides the argument of the product of z and w:
$$ \arg(zw) = \pi $$
Substitute the expression for w into the argument equation:
$$ \arg(z \cdot (-iz)) = \pi $$
$$ \arg(-i \cdot z^2) = \pi $$
Use the property of arguments where the argument of a product equals the sum of the individual arguments:
$$ \arg(-i) + \arg(z^2) = \pi $$
The argument of the purely imaginary number $$ -i $$ lies on the negative imaginary axis, which means:
$$ \arg(-i) = -\frac{\pi}{2} $$
Substitute this back into the equation:
$$ -\frac{\pi}{2} + \arg(z^2) = \pi $$
Use the argument property for powers where the exponent comes out as a multiplier:
$$ -\frac{\pi}{2} + 2\arg(z) = \pi $$
Isolate the term with the argument of z by adding $$ \frac{\pi}{2} $$ to both sides:
$$ 2\arg(z) = \pi + \frac{\pi}{2} $$
$$ 2\arg(z) = \frac{3\pi}{2} $$
Divide both sides by 2 to find the final value:
$$ \arg(z) = \frac{3\pi}{4} $$
Final Answer:
The value of the argument of z is $$ \frac{3\pi}{4} $$.
Click on the Email ☝️ to Watch the Video Solution
Create a FREE account and get:
Educational materials for JEE preparation