Pre Calc.
posted by Patrick .
Use the sum or difference identity to find the exact value of sin255 degrees.
My answer: (sqrt(2) sqrt(6)) / (4)
Find the value of tan (alphabeta), if cos alpha= 3/5, sin beta= 5/13, 90<alpha<180, and 90<beta<180.
My answer: 33/56
Which expression is equivalent to cos(pitheta)?
Is it cos theta?
Which expression is not equivalent to cos 2theta?
a. cos^2 theta sin^2 theta
b. 2cos^2 theta  1
c. 1  2sin^2 theta
d. 2sin theta cos theta
I would pick D.

correct on all counts, good job
For questions on finding "exact" values for certain trig ratios, a quick way to check your result is to simply evaluate your answer with a calculator, then compare it to the calculator result for the initial trig ratio
e.g. for yours I found (sqrt(2) sqrt(6)) / (4) to be .9659258
and sin 255 to be .9659258 , not bad eh?