Question 14

If $$\alpha$$ and $$\beta$$ ($$\alpha < \beta$$) are the roots of the equation $$(-2+\sqrt{3})(|\sqrt{x}-3|)+(x-6\sqrt{x})+(9-2\sqrt{3})=0,x\geq0\text{ then }\sqrt{\frac{\beta}{\alpha}}+\sqrt{\alpha\beta}$$ is equal to:

Let us set $$t = \sqrt{x}$$ so that $$x = t^2$$ and $$t \ge 0$$. Substituting into the given equation we get

$$(-2 + \sqrt{3})\,|t - 3| + (t^2 - 6t) + (9 - 2\sqrt{3}) = 0\,. $$

We will consider two cases depending on the sign of $$t - 3$$.

Case 1: $$t \ge 3\,. $$

Then $$|t - 3| = t - 3$$ and the equation becomes

$$(-2 + \sqrt{3})(t - 3) + t^2 - 6t + 9 - 2\sqrt{3} = 0\,. $$

Expand and collect like terms:

$$(-2 + \sqrt{3})t -(-2 + \sqrt{3})\cdot 3 + t^2 - 6t + 9 - 2\sqrt{3} = 0$$

$$\Rightarrow (-2 + \sqrt{3})t + 6 - 3\sqrt{3} + t^2 - 6t + 9 - 2\sqrt{3} = 0$$

Combine terms:

$$t^2 + \bigl(-2 + \sqrt{3} - 6\bigr)t + \bigl(6 + 9 - 3\sqrt{3} - 2\sqrt{3}\bigr) = 0$$

$$\Rightarrow t^2 + (-8 + \sqrt{3})\,t + (15 - 5\sqrt{3}) = 0\quad\,-(1)$$

Compute the discriminant:

$$\Delta = (-8 + \sqrt{3})^2 - 4(15 - 5\sqrt{3}) = 7 + 4\sqrt{3} = (\sqrt{3} + 2)^2\,. $$

Hence the roots are

$$t = \frac{8 - \sqrt{3} \pm (\sqrt{3} + 2)}{2}\,. $$

Thus

$$t = \frac{8 - \sqrt{3} + \sqrt{3} + 2}{2} = 5\quad\text{or}\quad t = \frac{8 - \sqrt{3} - \sqrt{3} - 2}{2} = 3 - \sqrt{3}\,. $$

Since we are in Case 1 with $$t \ge 3$$, only $$t = 5$$ is valid. This gives

$$x = t^2 = 25\,. $$

Case 2: $$0 \le t < 3\,. $$

Then $$|t - 3| = 3 - t$$ and the equation becomes

$$(-2 + \sqrt{3})(3 - t) + t^2 - 6t + 9 - 2\sqrt{3} = 0\,. $$

Expand and collect like terms:

$$(-2 + \sqrt{3})\cdot 3 -(-2 + \sqrt{3})t + t^2 - 6t + 9 - 2\sqrt{3} = 0$$

$$\Rightarrow -6 + 3\sqrt{3} + (2 - \sqrt{3})t + t^2 - 6t + 9 - 2\sqrt{3} = 0$$

Combine terms:

$$t^2 + \bigl(2 - \sqrt{3} - 6\bigr)t + \bigl(-6 + 9 + 3\sqrt{3} - 2\sqrt{3}\bigr) = 0$$

$$\Rightarrow t^2 + (-4 - \sqrt{3})\,t + (3 + \sqrt{3}) = 0\quad\,-(2)$$

The discriminant is again

$$\Delta = (-4 - \sqrt{3})^2 - 4(3 + \sqrt{3}) = 7 + 4\sqrt{3} = (\sqrt{3} + 2)^2\,. $$

So the roots are

$$t = \frac{4 + \sqrt{3} \pm (\sqrt{3} + 2)}{2}\,. $$

Thus

$$t = \frac{4 + \sqrt{3} + \sqrt{3} + 2}{2} = 3 + \sqrt{3}\quad\text{or}\quad t = \frac{4 + \sqrt{3} - \sqrt{3} - 2}{2} = 1\,. $$

In Case 2 with $$t < 3$$, only $$t = 1$$ is valid. This gives

$$x = t^2 = 1\,. $$

Therefore the two roots of the original equation (with $$\alpha < \beta$$) are

$$\alpha = 1\,,\quad \beta = 25\,. $$

We are asked to find

$$\sqrt{\frac{\beta}{\alpha}} + \sqrt{\alpha\,\beta} = \sqrt{\frac{25}{1}} + \sqrt{1 \cdot 25} = 5 + 5 = 10\,. $$

Final Answer: 10 (Option B).

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