This is not for homework, nor for a teacher to see, just a test correction so that I know what to do, or what I am doing wrong.

Use the sum or Difference formulas to find the exact value of each expression.

1. sin (165 degrees)

2. cos (5π/12)

I tried to use my calculator, a TI-89 ended up with the same answer both, and it was wrong unfortunately, and I was possibly wondering what I could do to get the correct answer.

my TI-89 gave me this:

((√3-1)*√(2))/(4)

Radical 3 - 1 * radical 2 all over 4.

And my best guess as the answer for both is [√6 + √2] / 4. Just not sure how to get that.

Edit: this might be my only trig question on here, as the 1st semester is almost gone, and I just wanted to figure these problems out.