- #1
Miike012
- 1,009
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Cos(x/2) = 1/2
Trig Identity: Cos(x/2)= +- (1+Cosx/2)^(1/2) ..How do you know wheather to use the plus or minus of (1+Cosx/2)^(1/2) ? Do you only use the positive one because of the positive 1/2?
Anyways...
((1+Cosx)/2)^(1/2) = 1/2
(1+Cosx)/2 = 1/4
1+Cosx = 1/2
Cosx = -1/2
Ref Angle is pi/3 --> Cos is neg in Quad 2 and 3
Thus x Must be 2pi/3 and 4pi/3
However... in the back of the book it says the answers are 2pi/3 and 10pi/3...
How did I not come up with 10pi/3? what did I do wrong?
Trig Identity: Cos(x/2)= +- (1+Cosx/2)^(1/2) ..How do you know wheather to use the plus or minus of (1+Cosx/2)^(1/2) ? Do you only use the positive one because of the positive 1/2?
Anyways...
((1+Cosx)/2)^(1/2) = 1/2
(1+Cosx)/2 = 1/4
1+Cosx = 1/2
Cosx = -1/2
Ref Angle is pi/3 --> Cos is neg in Quad 2 and 3
Thus x Must be 2pi/3 and 4pi/3
However... in the back of the book it says the answers are 2pi/3 and 10pi/3...
How did I not come up with 10pi/3? what did I do wrong?