Question

Use an angle sum identity to verify the identity cos2x=2cos^2x-1

Answer 1

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


cos(x+x) = 2*cos^2(x) - 1


cos(x)cos(x) - sin(x)sin(x) = 2*cos^2(x) - 1


cos^2(x) - sin^2(x) = 2*cos^2(x) - 1


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


cos^2(x) - 1 + cos^2(x) = 2*cos^2(x) - 1


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

Answer 2

The idea is to transform one side into the other

and you can only work on ONE side (leaving the other unchanged)

Answer 3

ok thank you I was always trying to work out both sides.

Answer 4

yw