SOLUTION: Solve the equation in the interval [0,2pi): 2 cos^2 theta + 3 cos theta + 1 = 0.

Question 451563: Solve the equation in the interval [0,2pi): 2 cos^2 theta + 3 cos theta + 1 = 0.
Answer by htmentor(1343) (Show Source): You can put this solution on YOUR website!
2 cos^2 theta + 3 cos theta + 1 = 0
To solve, let x = cos
So we have
2x^2 + 3x + 1 = 0
Solve using the quadratic formula:
x = (-3 +- sqrt(9 - 8))/4
This gives x = -1/2, x = -1
So we need to find the values of on the interval [0,2) which satisfy
cos = -1/2, -1
cos = -1, one of the zeros is
cos(2/3) = cos(4/3) = -1/2
So the zeros are: = (2/3),,(4/3)
The graph is below:

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