Question

• If cos(A - B) = cos A cos B + sin A sin B, then find cos 15°

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Answer 1

Answer:

cos( 45-30)=cos45cos30+sin45sin30=

1/root2×root3/2+1/root2×1/2=

(root3+1)/root2

Answer 2

Answer:

(√3+1)/2√2

Step-by-step explanation:

cos 15 = cos(45-30)

cos(45 - 30)= cos 45 cos 30 + sin 45 sin 30

                   =    1/√2 * √3/2 + 1/√2 * 1/2

                   =     (√3+1)/2√2