SA3 marksYear: 2025HardCBSE Class 10
trigonometrytrigonometric-identitiesproof
Question
Prove that: 1−cotθtanθ+1−tanθcotθ=1+secθ⋅cscθ
Solution
1
LHS =1−cosθ/sinθsinθ/cosθ+1−sinθ/cosθcosθ/sinθ=cosθ(sinθ−cosθ)sin2θ+sinθ(cosθ−sinθ)cos2θ
+1 mark2
=cosθ(sinθ−cosθ)sin2θ−sinθ(sinθ−cosθ)cos2θ=sinθ⋅cosθ(sinθ−cosθ)sin3θ−cos3θ
+0.5 marks3
=sinθ⋅cosθ(sinθ−cosθ)(sinθ−cosθ)(sin2θ+sinθcosθ+cos2θ)=sinθ⋅cosθ1+sinθcosθ
+1 mark4
=sinθcosθ1+1=1+secθ⋅cscθ = RHS
+0.5 marks