Prove: Â .

18
Evaluate, sec ²10 ^o– cot ²80 ^o+ .
19
Prove the following identity: . 21
Solve the following equation for 0° < θ ≤ 90°: 3 tan θ + cot θ = 5 cosecθ.
22
Solve for θ : =1, (θ ≠ 0).