Question

Упростите (1-sina)(sina+1)-cos2a​

Answer 1

$(1-sina)(1+sina)-cos2a=(1-sin^2a)-(cos^2a-sin^2a)=\\\\=1-sin^2a-cos^2a+sin^2a=1-cos^2a=sin^2a\\\\\\\star \; \; sin^2a+cos^2a=1\; \; \star$