Question

(1-sin(a))*(1+sin(a))+ cos²(a)-1=
помогите пж

Answer 1

$(1-sin (a))(1+sin(a))+cos^2 (a)-1=$

$(1^2-sin^2 (a))+cos^2 (a)-1$

$(1-sin^2 (a))+cos^2 (a)-1=$

$cos^2 (a)+cos^2 (a) -1=$

$2cos^2 (a) -1=cos(2a)$