Math
posted by Kate .
Which of the following is a solution to the trigonometric equation
2cos2 x  5cos x + 2 = 0?
A) 240 degrees
B) 135 degrees
C) 270 degrees
D) 90 degrees

Math 
Reiny
I will read that as
2cos^2 x  5cos x + 2 = 0
(2cosx  1)(cosx  2) = 0
cosx = 1/2 or cosx = 2, the last part of course is not possible
so cosx = 1/2
x = 60° or 300°
So none of your choices work.
Both of my answers work in the original equation.
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