If you're finding f(pi), just substitute x = pi and simplify...
i think he is asking about f(pi) and not f1(pi) so u have to find f(x) by integrating the gradient and then just substitute f(0)=1 to find the value of the constant
i think he is asking about f(pi) and not f1(pi) so u have to find f(x) by integrating the gradient and then just substitute f(0)=1 to find the value of the constant