trigonometry - Simple trigonometric identity proof: $sin^4x-cos^4x=2sin^2x-1$

How would you verify that this trigonometric equation is an identity?

$$\sin^4x-\cos^4x=2\sin^2x-1? $$

The 4th powers are really throwing me off, and i'm still fairly new to this and there is no clear identity from the start like $\cos^2x + \sin^2x=1$

Thanks