Q8 of 58 Page 8


Prove that: cos (81 °+ θ) = sin (9° - θ).


L.H.S = cos (81° + θ)
= cos [90° - (9° - θ)]
= sin (9° - θ)

(using cos (90° - ϕ ) = sin ϕ )
= R.H.S.

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