Question

Using the formula cos(A-B)cosA cosB + sinA.sinB find the value of cos 15

Answer 1

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Answer 2

Answer:

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We know that

cos (a-b) = cos a * cos b + sin a *sin b

cos 15 = cos (45–30)

=> cos 15 = cos 45 * cos 30 + sin 45 * sin 30

=> cos 15 = (1/√2)* (√3/2) + (1/√2)*(1/2)

=> cos 15 = (√3 + 1 )/2√2