Question

tg/1-tg^2a*ctg^2a-1/ctga

Answer 1

1+ tg^2 a = 1/cos^2 a
1+ ctg^2 a = 1/sin^2 a
1/ cos^2 a * sin^2 a/1 = tg^2 a.
tg^2 a = tg^2 a.