Question

sin^4-cos^4=sin^2-cos^2 докажите тождество

Answer 1

$sin^4x-cos^4x=sin^2x-cos^2x \\(sin^2x-cos^2x)(sin^2x+cos^2x)=sin^2x-cos^2x \\(sin^2x-cos^2x)*1=sin^2x-cos^2x \\sin^2x-cos^2x=sin^2x-cos^2x$