Question ID: #788
If $\alpha$ and $\beta$ $(\alpha < \beta)$ are the roots of the equation $(-2+\sqrt{3})(|\sqrt{x}-3|) + (x-6\sqrt{x}) + (9-2\sqrt{3}) = 0, x \ge 0$, then $\sqrt{\frac{\beta}{\alpha}}+\sqrt{\alpha\beta}$ is equal to:
- (1) 8
- (2) 9
- (3) 10
- (4) 11
Solution:
Let the given equation be:
$$ (\sqrt{3}-2)|\sqrt{x}-3| + (x-6\sqrt{x}+9) – 2\sqrt{3} = 0 $$
Notice that $x-6\sqrt{x}+9 = (\sqrt{x}-3)^2 = |\sqrt{x}-3|^2$.
Let $u = |\sqrt{x}-3|$. The equation becomes:
$$ (\sqrt{3}-2)u + u^2 – 2\sqrt{3} = 0 $$
$$ u^2 – (2-\sqrt{3})u – 2\sqrt{3} = 0 $$
We factorize the quadratic in $u$:
$$ u^2 – 2u + \sqrt{3}u – 2\sqrt{3} = 0 $$
$$ u(u-2) + \sqrt{3}(u-2) = 0 $$
$$ (u-2)(u+\sqrt{3}) = 0 $$
So, $u = 2$ or $u = -\sqrt{3}$.
Since $u = |\sqrt{x}-3|$ is an absolute value, it must be non-negative.
Therefore, $u = 2$ is the only valid solution.
$$ |\sqrt{x}-3| = 2 $$
$$ \sqrt{x}-3 = 2 \quad \text{or} \quad \sqrt{x}-3 = -2 $$
$$ \sqrt{x} = 5 \quad \text{or} \quad \sqrt{x} = 1 $$
$$ x = 25 \quad \text{or} \quad x = 1 $$
Given $\alpha < \beta$, we have $\alpha = 1$ and $\beta = 25$.
We need to find $\sqrt{\frac{\beta}{\alpha}} + \sqrt{\alpha\beta}$:
$$ \sqrt{\frac{25}{1}} + \sqrt{1 \cdot 25} $$
$$ = \sqrt{25} + \sqrt{25} $$
$$ = 5 + 5 = 10 $$
Ans. (3)
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