View Compilation Error

0_0_34158225_2033.cpp: In function 'int main()':
0_0_34158225_2033.cpp:2:19: error: 'acos' was not declared in this scope
 #define PI acos(-1)
                   ^
0_0_34158225_2033.cpp:10:39: note: in expansion of macro 'PI'
   ans = (n - 1)*(r*r*sin((180.0 / n)*(PI / 180.0))*cos((180.0 / n)*(PI / 180.0))) + r*r*sin((180.0 / n)*(PI / 180.0));//度数乘以pi/180
                                       ^
0_0_34158225_2033.cpp:10:50: error: 'sin' was not declared in this scope
   ans = (n - 1)*(r*r*sin((180.0 / n)*(PI / 180.0))*cos((180.0 / n)*(PI / 180.0))) + r*r*sin((180.0 / n)*(PI / 180.0));//度数乘以pi/180
                                                  ^
0_0_34158225_2033.cpp:10:80: error: 'cos' was not declared in this scope
   ans = (n - 1)*(r*r*sin((180.0 / n)*(PI / 180.0))*cos((180.0 / n)*(PI / 180.0))) + r*r*sin((180.0 / n)*(PI / 180.0));//度数乘以pi/180
                                                                                ^