If =y, then  isalso y.

8
Prove that: cos (81 ^°+ θ) = sin (9° - θ).
9
Prove that: sin θ cos (90°- θ) + cos θ sin (90° - θ) = 1.
11
Prove:  = tan ² ϕ 12
Prove: (sec θ - tan θ) ²= .