(1+tg^2 a+1/sin^2 a)•sin^2 a cos^2a=1

Question

(1+tg^2 a+1/sin^2 a)•sin^2 a cos^2a=1

Answer 1

(1+tg²a+1/sin²a)*sin²a*cos²a=1
(1/cos²a+1/sin²a)*sin²a*cos²a=1
(sin²a+cos²a)/(cos²a*sin²a)*sin²a*cos²a=1
1=1
Тождество доказано