SA3 marksYear: 2024HardCBSE Class 10
trigonometryidentitiesproof
Question
Prove that: 1−cotθtanθ+1−tanθcotθ=1+secθcscθ
Solution
1
LHS =1−sinθcosθcosθsinθ+1−cosθsinθsinθcosθ
+0.5 marks2
=cosθsinθ×sinθ−cosθsinθ+sinθcosθ×cosθ−sinθcosθ
=sinθ−cosθ1(cosθsin2θ−sinθcos2θ)
+1 mark3
=sinθ−cosθ1×sinθcosθsin3θ−cos3θ
=(sinθ−cosθ)sinθcosθ(sinθ−cosθ)(sin2θ+cos2θ+sinθcosθ)
+1 mark4
=sinθcosθ1+sinθcosθ=sinθcosθ1+1=1+secθcscθ = RHS
+0.5 marks