Q: Find the point on the line -5 x + 3 y + 5 =0 which is closest to the point ( -3, 3 ).

Solution: I know I have to use the distance formula, and I have to plug in the x and y with x and f(x);

therefore I got to here d = (x+3)^2+[(5x-5)/3-3]^2;

and f'(x) = 2(x+3) + (10/3)(5x-14)/3;

then I have no idea what to do, as our prof didn't bother to explain it afterward...

Any idea how to solve it?