kill(all)$

van=facebook.com/LearningCalulus$

f(x,y):=1-sqrt(x^2+y^2);

g(r,%theta):=1-r;

'integrate('integrate('g(r,%theta)*r,r,0,1),%theta,0,2*%pi)=
 integrate( integrate( g(r,%theta)*r,r,0,1),%theta,0,2*%pi);

k*rhs(%)=1;

first(solve(%,k));