1. Given. F(x) = 4x/(x^2+1) 2. Problem Find all points (x,y) where the function has a horiztonal tangent line 3. Attempt I took the derivative of F(x) and came to (-4x^2+4)/(x^2+1)^2 I set it equal to zero and found an x value of 1. I used that x value and plugged it into the original function, so f(1), and got a Y value of 2, but according to my professor this was not correct. However I asked him this after the test. It was a test question and on the test I stated at no point does the function have a horizontal tangent line. I figured I was wrong because after the test I redid the problem and came to (1,2). Although as stated, my professor said (1,2) was incorrect. I haven't got my test back, so maybe there was no solution and I did the problem correctly originally, but I think there is a solution. Thanks!