View Compilation Error

0_0_2096052_32709.cpp: In function `int main()':
0_0_2096052_32709.cpp:8: error: `d' undeclared (first use this function)
0_0_2096052_32709.cpp:8: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2096052_32709.cpp:8: error: `sqrt' undeclared (first use this function)
0_0_2096052_32709.cpp:11: error: `a' undeclared (first use this function)