View Compilation Error

0_0_36876742_11942.cpp: In function 'int main()':
0_0_36876742_11942.cpp:28:8: error: 'x2' was not declared in this scope
   if(f(x2)<y0 && f(xb)<=y2 && f(xa)>y0){
        ^
0_0_36876742_11942.cpp:28:20: error: 'xb' was not declared in this scope
   if(f(x2)<y0 && f(xb)<=y2 && f(xa)>y0){
                    ^
0_0_36876742_11942.cpp:28:33: error: 'xa' was not declared in this scope
   if(f(x2)<y0 && f(xb)<=y2 && f(xa)>y0){
                                 ^