1.

Prove that cos(15°)​

Answer»

cos 15°

= cos (45 - 30)

It is of the FORM cos (A - B)

cos (A - B) = cos A cos B + SIN A sin B

cos 45° cos 30° + sin 45° sin 30°

(1/√2)(√3/2) + (1/√2)(1/2)

√3/2√2 + 1/2√2

(√3 + 1)/2√2


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