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Question: The equation \(\sec^{2}\theta = \frac{4xy}{(x + y)^{2}}\) is only possible when...

The equation sec2θ=4xy(x+y)2\sec^{2}\theta = \frac{4xy}{(x + y)^{2}} is only possible when

A

x=yx = y

B

x<yx < y

C

x>yx > y

D

None of these

Answer

x=yx = y

Explanation

Solution

cos2θ1\because\cos^{2}\theta \leq 1

sec2θ=4xy(x+y)214xy(x+y)2(xy)20\sec^{2}\theta = \frac{4xy}{(x + y)^{2}} \geq 1 \Rightarrow 4xy \geq (x + y)^{2} \Rightarrow (x - y)^{2} \leq 0Which

is possible only when x=yx = y (x,yR)(\because x,y \in R)