Homework Help: Pre Cal.

Posted by Danny on Tuesday, June 16, 2009 at 9:54am.

1. Use half-angle 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+ 3y-5=0 in normal form?
(-2sqrt(13)/13)x - (3sqrt(13)/13)y + 5sqrt(13)/13) = 0

Pre Cal. - Reiny, Tuesday, June 16, 2009 at 11:18am
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)

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