Question

Find cos 15 using cos (a-b) =cosa cos b+sina sin b

Answer 1

Hey mate Your answer is here

Cos15°

can be written as

cos(45-30)°

so we can use

cos(a-b)=CosACosB+SinASinB. as given

Therefore

Cos(45-30)°

=Cos45°Cos30°+Sin45°Sin30°

=(1/√2)(√3/2)+(1/√2)(1/2)

=(√3/2√2) + (1/2√2)

= (√3+1)

2√2

Thank you

Regards ☺️