trig

How many solutions does the equation cos(x) + cos(−x) = 0 have if 0 < x < 2pi?
(Radian measure is assumed for x.)
(A) infinitely many (B) 1 (C) 2 (D) 3 (E) None of the above.

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asked by dat
  1. Since cos(-x) = cos(x) for all x
    cosx + cos(-x) = 0
    2cosx = 0
    cosx = 0
    x = π/2 or x = 3π/2 (90° and 270°)

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    posted by Reiny

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