1) Manipulating the Left side
cost · sect - cos²t (Note: sect= 1/cost, cos²t = 1-sin²t)
cost · (1/cost) - (1 - sin²t)
1 - 1 + sin²t
0 + sin²t
sin²t
2) Manipulating the Left side
sinФ · cotФ (Note: cotФ = cosФ/sinФ)
sinФ · (cosФ/sinФ)
(sinФ · cosФ)/sinФ
cosФ
