Question 19

If $$\sqrt{(1 - p^2)(1 - q^2)} = \frac{\sqrt{3}}{2}$$, then what is the value of $$\sqrt{2p^2 + 2q^2 + 2pq} + \sqrt{2p^2 + 2q^2 - 2pq}$$?

Solution

From $$\sqrt{(1-p^2)(1-q^2)}=\frac{\sqrt{3}}{2}\ $$

we can say that :

$$(1-p^2)(1-q^2)=\frac{3}{4}=\left(1-0^2\right)\left(1-\frac{1}{2^2}\right)\ .$$

So, either p/q=0/(1/2) .

So, 

$$\sqrt{2p^2+2q^2+2pq}+\sqrt{2p^2+2q^2-2pq}=\sqrt{\ 0+2\times\frac{1}{4}+0}+\sqrt{0+2\times\frac{1}{4}-0}=\sqrt{\frac{1}{2}}+\sqrt{\frac{1}{2}}=\frac{2}{\sqrt{2}}=\sqrt{2}.$$

So, B is correct choice.


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