Tg^2a + ctg^2a+2- 1/cos^2a

Question

Tg^2a + ctg^2a+2- 1/cos^2a

Answer 1

Cos²a+sin²a=1 |:cos²a
1+tg²a=1/cos²a
ctg²a+1=1/sin²a

tg²a+ctg²a+2-(1+tg²a)=tg²a+ctg²a+2-1-tg²a=ctg²a+1=1/sin²a