Q. 3 G

# Prove that :<

Answer :

sin 80° – cos 70° = cos 50°

sin 80° = cos 50° + cos 70°

Take RHS:

cos 50° + cos 70°   = 2 cos 60° cos (-10°)

{cos (-A) = cos A} = cos 10°

= cos (90° - 80°)

{cos (90° - A) = sin A}

= sin 80°

= L.H.S

Hence Proved

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