Solve the equation cosx= -0.4 on the interval 0≤x＜2π._数学解答

Solve the equation cosx= -0.4 on the interval 0≤x＜2π.

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解答

cosx = -0.4arccos(-0.4) ≈ 1.98 radiansx = 2nπ±arccos(-0.4),n can be any integern = 0:x = 2nπ+arccos(-0.4) = 1.98n = 1:x = 2nπ－arccos(-0.4) = 2π - 1.98 = 4.30