Question

How do you use the sum and difference formula to simplify cos15?

Answer 1

cos(45°-30°)=cos45°(cos30°)+sin45°(sin30°)

cos(45°-30°)=1/√2(√3/2)+1/√2(1/2)

cos(45°-30°)=√3+1/2√2

cos(15°)=√3+1/2√2