Question

2tg^2a×cos^2a-sin^2a

Answer 1

$2 tg^{2} a* cos^{2}a- sin^{2}a=2 \frac{ sin^{2}a }{ cos^{2}a }* cos^{2}a- sin^{2}a= \\ =2sin^{2}a-sin^{2}a=sin^{2}a$