Homework Help: Inflection points

Posted by Kay on Tuesday, November 17, 2009 at 12:14am.

Consider the function f(x)=12x^5+30x^4–300x^3+2. f(x) has inflection points at (reading from left to right) x=D,E, and F. where D is___, E is____, and F is____.

I took the second derivative of the function and got 120x(2x^2+3x-15). From that I set it to equal and tried finding x. One is obviously zero.

Then I tried using the quadratic formula to get the other two x's. I got [-3 + sqrt(129)]/4 and [-3 - sqrt(129)]/4

However I plugged the answer into my online homework site and it says that is incorrect. Can someone help?

Math - Writeacher, Tuesday, November 17, 2009 at 7:11am
Assistance needed.

Please type your subject in the School Subject box. Any other words are likely to delay responses from a teacher who knows that subject well.
Inflection points - bobpursley, Tuesday, November 17, 2009 at 8:39am
I agree with you.
Inflection points - Kay, Tuesday, November 17, 2009 at 9:55pm
Writeacher, thanks for the tip...I was never really sure whether I was supposed to type my actual class subject or the subject material. If it's ok, I might submit this question again with a different school subject.

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