Question

Докажите тождества пожалуйста

Answer 1

$sin^{4}(a)-cos^{4}(a)=sin^{2}(a)-cos^{2}(a)$ ,

$(sin^{2}(a)-cos^{2}(a))(sin^{2}(a)+cos^{2}(a)) = sin^{2}(a)-cos^{2}(a)$ ,

$1 * sin^{2}(a)-cos^{2}(a) = sin^{2}(a)-cos^{2}(a)$ ,

$sin^{2}(a)-cos^{2}(a) = sin^{2}(a)-cos^{2}(a)$