posted by Eve on .
Find the points on the graph of f where the tangent line is horizontal.
After I did the quotient rule I got:
Then of course I know you set that equal to 0, but I do not know how to set it up or "finalize" the problem because of the denominator. Please help!
((x^2+25)(1)-(x)(2x))/(x^2+25)^2 = 0
(25-x^2)/(x^2+25)^2 = 0
As long as x^2+25 <> 0 then you can multiply both sides by the denominator
(25-x^2) = 0
x^2 = 25
x = ±5
( Check: 25+25<>0 .. okay)
Find y when x=-5 and x=+5. These are your points
does that go into the derivative equation or the original?