The function f(x,y) is defined for all real numbers x,y. It satisfies f(x,0)=ax (where a is a non-zero constant) and if (c,d) and (h,k) are distinct points such that f(c,d)=f(h,k), then f(x,y) is constant on the line through (c,d) and (h,k). Show that for any real b, the set of points such that f(x,y)=b is a straight line and that all such lines are parallel. Show that f(x,y)=ax+by, for some constant b. functionalgebraLinear Function