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## Homework Statement

This is a question from my test paper.

If sec [itex]\theta[/itex]=[itex]\frac{4xy}{(x+y)^2}[/itex], where x,y [itex]\in[/itex] R, then

(a)x,y [itex]\in[/itex] R

^{+}

(b)x,y [itex]\in[/itex] R

^{-}

(c)x=y[itex]\neq[/itex]0

(d)x[itex]\in[/itex]R

^{+}, y[itex]\in[/itex]R

^{-}

## Homework Equations

## The Attempt at a Solution

I don't understand what i have to do and where should i start with?