Question

sin²(п+a)+cos²(a-п)+ctg²(п/2-а) ??​

Answer 1

$\displaystyle\bf\\Sin^{2} \Big(\pi +\alpha\Big )+Cos^{2} \Big(\alpha -\pi \Big)+Ctg^{2} \Big(\frac{\pi }{2} -\alpha \Big)=\underbrace{Sin^{2} \alpha +Cos^{2} \alpha}_{1}+tg^{2} \alpha = \\\\\\=1+tg^{2} \alpha =\frac{1}{Cos^{2} \alpha }$