Question

Find the value of cos15, using the result cos(A-B)=cosAcosB+sinAsinB​

Answer 1

Answer:

Step-by-step explanation:

We know that cos(A-B)=cosAcosB+sinAsinB

we can write 15 as (45-30)

cos 15 = cos(45-30)

cos(45-30) = cos45cos30+sin45sin30

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

                  = (√3/2√2) + (1/2√2)

                  =(√3+1)/2√2