Question

Assume cos (A-B)=cosA cosB +cosA sinB ,find cos 15° when A=45°,B=30°

Answer 1

Answer: (√3 + 1) / 2√2

Step-by-step explanation:

Here's the answer you are looking for

if cos(a-b)=cosa cosb + sina sinb and we have to find cos15

15 can be expressed as (45 - 30)

So,

cos 15 = cos (45 - 30)

= cos45cos30 + sin45sin30

= (1/√2)(√3/2) + (1/√2)(1/2)

= √3/2√2 + 1/2√2

= (√3 + 1) / 2√2