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What is the right choice for question 25) ? http://postimg.org/image/jmc3afzb9/

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What is the right choice for question 25) ?

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Posted (Answer #1)

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`1-2sin^2x`

We know that;

`sin^2x+cos^2x =1`

`1-2sin^2x`

`= (sin^2x+cos^2x)-2sin^2x`

`= sin^2x-2sin^2x+cos^2x`

`= cos^2x-sin^2x`

So the correct choice is b).

Note

Actually `(1-2sin^2x) ` means `cos2x` .

`Cos2x` can be written in the following forms.

`cos2x = 1-2sin^2x = 2cos^2-1 = cos^2x-sin^2x`

Sources:

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