View Compilation Error

0_0_11635809_21980.cpp:32: error: `acos' was not declared in this scope
0_0_11635809_21980.cpp: In function `bool equ(double, double)':
0_0_11635809_21980.cpp:36: error: `fabs' undeclared (first use this function)
0_0_11635809_21980.cpp:36: error: (Each undeclared identifier is reported only once for each function it appears in.)