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 Summary ```#include double acos ( double x); /* number to calculate arc cosine of */ ``` Description The acos function calculates the arc cosine of the floating-point number x whose value must be between -1 and 1. The floating-point value returned by acos is a number in the range 0-π. Return Value The acos function returns the arc cosine of x. For x ∈ [-1, 1], acos(x) → [0, π]. For x ∈ (-∞, -1) ∪ (1, ∞), acos(x) → NaN. See Also Example ```#include #include /* for printf */ void tst_acos (void) { float x; float y; for (x = -1.0; x <= 1.0; x += 0.1) { y = acos (x); printf ("ACOS(%f) = %f\n", x, y); } } ```

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