If cos x + sin x = a , (- (pi)/(2) lt x ...

If `cos x + sin x = a , (- (pi)/(2) lt x lt - (pi)/(4))`, then `cos 2 x ` is equal to

A

`a^(2)`

B

`a sqrt((2-a))`

C

`a sqrt((2+a))`

D

`asqrt((2-a^(2)))`

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The correct Answer is:

D

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