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

### 1 Answer | Add Yours

`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:**