Q2 of 123 Page 9

Prove that:

4(cos310o + sin320o) = 3 (cos10o + sin20o)

We know that


⇒ sin (3× 20°)=cos (3× 10°)


⇒ 3sin 20°–4sin320°=4cos310°–3cos 10°


(as sin 3θ=3sin θ–4sin3 θ and cos 3θ =4cos3θ–3cosθ)


⇒ 4(cos310°+sin320°)=3(sin 20°+cos 10°)


LHS=RHS


Hence proved


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