Math - Solving for Trig Equations

For the following equation, why cannot I not solve it? I keep getting an error.

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2cosx - 3 = 0
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I first isolated for "x"
2cosx-3 = 0
(2cosx/2) = (3/2)
x = cos^-1(3/2)
x = error? why?

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My textbook answer:
30 and 330 degrees
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  1. Make sure you copied the question correctly.
    The way it stands
    cos x = 3/2 has indeed no solution

    (the sine and cosine function does not exceed a value >1 or < -1

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