It is proved that for any angle α, cos ^ 4 α - Sin ^ 4 α = cos 2 α by synthesis or analysis Mathematics is proved by synthesis or analysis: for any angle α, cos ^ 4 α - Sin ^ 4 α = Cos2 α It's better to use the inverse method | Math enthusiast | Mathematical art

It is proved that for any angle α, cos ^ 4 α - Sin ^ 4 α = cos 2 α by synthesis or analysis Mathematics is proved by synthesis or analysis: for any angle α, cos ^ 4 α - Sin ^ 4 α = Cos2 α It's better to use the inverse method

cos^4α-sin^4α=（cos^2α+sin^2α）（cos^2α-sin^2α）=cos^2α-sin^2α=cos2α
If you come backwards, that's the inverse method