Question

Simplify (sinx - cosx) (sinx + cosx)

Answer 1

[sin(x) - cos(x)][sin(x) + cos(x)]
sin(x)[sin(x) + cos(x)] - cos(x)[sin(x) + cos(x)]
sin(x)[sin(x)] + sin(x)[cos(x)] - cos(x)[sin(x)] - cos(x)[cos(x)]
sin²(x) + sin(x)cos(x) - sin(x)cos(x) - cos²(x)
sin²(x) - cos²(x)
-cos(2x)