Question

Question #3d3b0

Answer 1

`10(cos^2x-sin^2x)-5`

Explanation:

The double angle formula for `cos 2x` is `cos 2x = cos^2x-sin^2x`. With that in mind...

`10cos2x -5 = 10(cos^2x-sin^2x)-5`

To derive the double angle formula for `cos2x`, instead rewrite it as `cos(x+x)`, and use the sum of two angles formula:

`cos(a+b)=cosacosb - sinasinb`

And set a=b=x

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