Pre Cal.
posted by Danny on .
1. Use halfangle identity to find the exact value of cos165.
MY ANSWER: (1/2)sqrt(2+sqrt(3))
2. Solve 2 sin x + sqrt(3) < 0 for 0<= x<2pi.
MY ANSWER: (4pi/3)< x < (5pi/3)
3.Write the equation 2x+ 3y5=0 in normal form?
(2sqrt(13)/13)x  (3sqrt(13)/13)y + 5sqrt(13)/13) = 0

your first one cannot be right since your result <  1,
and the cosine and sine of any angle cannot be greater than 1 or less than 1.
there are several ways to split up 165
1. 165 = 180  15
2. 165 = 90 + 75, but 75 = 45 + 30
unless I misses an obvious combination, it looks like you have do this in 2 steps
third question is correct, if you follow the formula
(don't know why anybody would want to write an equation which looks very neat and clean in such a complex looking form)