The above is a standard "Two Column Proof". However, we are not trying to prove sin' 0 - sin 0. Therefore, this "Two Column Proof" will not be accepted in our course. Instead, we need to prove either 1) LHS (left hand side) = RHS (right hand side) or 2) LHS = an expression and RHS also equal the same expression as LHS. Here is one of the accepted proof: Proof: 1 - cos 0 1 - cos 0 1 + cos 0. 1 - cos2 0 sin2 0 sin 0 LHS = = RHS sin 0 sin 0 1 + cos 0 sin 0 . (1 + cos 0) sin 0 . (1 + cos () 1 + cos 0 Please keep this in mind and try the following questions: Prove the following identities: cos 0 sin 0 1) 1 - tan 0 + 1 - cot 0 = sin 0 + cos 0 1 1 2) 1 - sin 0 + 2 sec2 0 1 + sin 0 1 3) = 1 + tan2 0 1 - sin2 0