Instead of -1/10 I have -1/3 is that wrong?

Question

R(x)=-1/3(x)^2+100(x) My teachers tells us to use -1/3 instead of -1/10 is this correct or is my teacher wrong? Or am I doing my problems wrong?

Answer 1

You would use -1/3 in most calculations. What is it you are trying to do though? If you are finding the x-intercepts (zeros), you would factor out an x to get f(x) = x(-1/3x + 100) then set f(x) = 0 and solve for x. If you are trying the find the vertex, you would use a = -1/3 and b = 100 then use x = -b/2a.