acos(3) Library Functions Manual acos(3) acos, acosf, acosl - (libm -lm) #include double acos(double x); float acosf(float x); long double acosl(long double x); glibc ( feature_test_macros(7)): acosf(), acosl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE x x. x [0, pi]. x (NaN) NaN. x +1 +0. x NaN ( ). x [-1, 1] NaN. math_error(7) . : : x [-1, 1] errno EDOM. (FE_INVALID). attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |acos(), | | MT-Safe | |acosf(), | | | |acosl() | | | +------------+------------------------------------+--------------------+ C11, POSIX.1-2008. C99 POSIX.1-2001. double C89 SVr4 4.3BSD. asin(3), atan(3), atan2(3), cacos(3), cos(3), sin(3), tan(3) 3 . . : . 6.18 8 2026 acos(3)