Question

(ctga * 1/cosa)² - 2sin²a -2 cos²a= (буду очень благодарен)

Answer 1

$(Ctg\alpha *\frac{1}{Cos\alpha})^{2}-2Sin^{2}\alpha-2Cos^{2}\alpha=\frac{Cos^{2}\alpha}{Sin^{2}\alpha}*\frac{1}{Cos^{2}\alpha}-2(Sin^{2}\alpha+Cos^{2}\alpha)=\frac{1}{Sin^{2}\alpha} -2*1=1+Ctg^{2}\alpha-2=Ctg^{2}\alpha-1$