    const std = @import("../../std.zig");
    const testing = std.testing;
    const math = std.math;
    const cmath = math.complex;
    const Complex = cmath.Complex;

    /// Returns the cosine of z.
    pub fn cos(z: anytype) Complex(@TypeOf(z.re)) {
        const T = @TypeOf(z.re);
        const p = Complex(T).init(-z.im, z.re);
        return cmath.cosh(p);
    }

    const epsilon = 0.0001;

    test "complex.ccos" {
        const a = Complex(f32).init(5, 3);
        const c = cos(a);

        try testing.expect(math.approxEqAbs(f32, c.re, 2.855815, epsilon));
        try testing.expect(math.approxEqAbs(f32, c.im, 9.606383, epsilon));
    }