Question

sin 2 99 + cos 2 81 + ctg 2 315 sos

Answer 1

$sin^299+cos^281+ctg^2315=\\=sin^2(90+9)+cos^2(90-9)+ctg^2(270+45)=\\=(cos^29+sin^29)+tg^245=1+tg^245=1+1^2=2$