Prove that: tan69∘+tan66∘1−tan69∘tan66∘=−1
LHS:tan69∘+tan66∘1−tan69∘tan66∘ =tan(69∘+66∘) =tan(135∘) =tan(90∘+45∘) =−cot45∘ [∵ tanθ is negative in second quadrant] =-1 =RHS therefore LHS=RHS Hence proved.