View Compilation Error

0_0_11060084_7417.cpp:3: error: `acos' was not declared in this scope
0_0_11060084_7417.cpp: In function `int main()':
0_0_11060084_7417.cpp:16: error: `sort' undeclared (first use this function)
0_0_11060084_7417.cpp:16: error: (Each undeclared identifier is reported only once for each function it appears in.)