Prove that : sec(3π2−θ)sec(θ−5π2)+tan(5π2+θ)tan(θ−3π2)=−1
LHS=sec(3π2−θ)sec(θ−5π2)+tan(5π2+θ)tan(θ−3π2)
=sec(3π2−θ)sec(−(5π2−θ))+tan(5π2−θ)tan[−(3π2−θ)]
=−cosecθ.sec(5π2−θ)=cotθ×(−)tan(3π2−θ)
⎡⎢ ⎢ ⎢ ⎢⎣∵(sec(3π2−θ))=−cosecθ,sec(−θ)=secθ,tan(5π2+θ)=−cotθand tan(−θ)=−(tanθ)⎤⎥ ⎥ ⎥ ⎥⎦
=−cosecθ×cosecθ−cotθ×(−1)×cotθ
⎡⎢⎣∵(sec(5π2−θ))=−cosecθand tan(3π2−θ)=cotθ⎤⎥⎦
=−cosec2θ×cot2θ
=−cosec2θ×cosec2θ−1[∵cosec2θ=1+cot2θ]
=-1 =RHS Hence proved.