Posted by t54 on Monday, April 4, 2011 at 6:17pm.
I bet it said "find the exact value"
sin(-15) = sin(30-45)
= sin30cos45 - cos30sin45
= (1/2)(√2/2) - (√3/2)(√2/2) = (√2 - √6)/4
tan(165) = tan(120+45)
= (tan120 + tan45)/(1-tan120tan45)
tan 120 = -tan60 = -√3
so back into the above result
= (-√3 + 1)/(1 - (-√3)(1)) = (1-√3)/(1+√3)