all Python 3cmathfunction

cmath.cos()

trigonometry

The cosine of a complex argument; cos(i·x) equals cosh(x), so it can be arbitrarily large.

Syntax

cmath.cos(z)

Even for a real input the answer is complex and often carries a negative zero: cos(0) prints as (1-0j). That -0j equals zero, and cos(0) == 1 is True, but the printed text is confusing and breaks string comparisons in tests. Use math.cos for real angles; cmath is for genuinely complex arguments.

Examples

import cmath
print(cmath.cos(0), cmath.cos(0) == 1)  # → (1-0j) True
print(cmath.cos(1j))  # → (1.5430806348152437-0j) — это cosh(1)

See also

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