Question

Verify the identity: cos^2x -sin^2x=1-2sin^2x

Is this cos(2x)=cos(2x) ???

Answer 1

cos^2x = 1-sin^2x.

1-sin^2x - sin^2x = 1 - 2sin^2x.

hence cos^2x-sin^2x = 1-2sin^2x.

Also, cos^2x - sin^2x

=> cos^2x - (1-cos^2x)

=> 2cos^2x -1 = cos 2x.

Hence cos^2x - sin^2x also equals cos 2x.

Answer 2

So yes then...?

Answer 3

lol the sum is done!?

of course cos 2x = cos 2x. :P

Answer 4

That's what I thought ha. Thanks