atan(3) Library Functions Manual atan(3) atan, atanf, atanl - LIBRARY Math library (libm, -lm) #include double atan(double x); float atanf(float x); long double atanl(long double x); glibc (. feature_test_macros(7)): atanf(), atanl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE x; , x. x ; [-pi/2, pi/2]. x NaN, NaN. x +0 (-0), +0 (-0). x ( ), +pi/2 (-pi/2). . attributes(7). +----------------------------+----------------------------------------------------------+--------------------------+ | | | | +----------------------------+----------------------------------------------------------+--------------------------+ |atan(), atanf(), atanl() | | MT-Safe | +----------------------------+----------------------------------------------------------+--------------------------+ C11, POSIX.1-2008. C99, POSIX.1-2001. , double, SVr4, 4.3BSD, C89. . acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3) Dmitry Bolkhovskikh Yuri Kozlov ; GNU 3 , . . , , . Linux man-pages 6.06 31 2023 . atan(3)