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This page displays the COHERENT manpage for acos() [Calculate inverse cosine].
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acos() -- Mathematics Function (libm) Calculate inverse cosine #include <math.h> double acos(arg) double arg; acos() calculates the inverse cosine. arg should be in the range of -1.0, 1.0. It returns the result, which is in the range of from zero to pi radians. Example This example demonstrates the mathematics functions acos(), cabs(), and tan(). #include <errno.h> #include <math.h> #include <stdio.h> #include <stdlib.h> #define display(x) dodisplay((double)(x), #x) dodisplay(value, name) double value; char *name; { if (errno) perror(name); else printf("%10g %s\n", value, name); errno = 0; } main() { extern char *gets(); double x; char string[64]; for(;;) { printf("Enter number: "); if(gets(string) == NULL) break; x = atof(string); display(x); display(acos(cos(x))); display(cabs(sin(x),cos(x))); } } See Also cos(), errno, errno.h, libm, perror() ANSI Standard, §7.5.2.1 POSIX Standard, §8.1