Question

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

Answer 1

see below

Explanation:

`cos 15^@=cos(45^@-30^@)`

`=cos45^@cos30^@+sin45^@sin30^@`

`=sqrt2/2* sqrt3/2+sqrt2/2 *1/2`

`=sqrt6/4+sqrt2/4`

`=(sqrt6+sqrt2)/4`