Question

How do you prove the identity `-sin^2x = 2cosx - 2`?

Answer 1

The given expression is not a valid indentity
`color(white)("XXXX")`(It can not be proven).

Explanation:

Consider, for example `x=pi/2`

`color(white)("XXXX")` `-sin^2(pi/2) = -1`

`color(white)("XXXX")` `2cos(pi/2)-2 = -2`

`-sin(pi/2) != 2cos(pi/2)-2`