Register to reply

Finding intercepts of a cubic function

by Arya1127
Tags: cubic, function, intercepts
Share this thread:
Nov14-10, 05:59 PM
P: 1
Hey guys, new member here. I've decided to join this forum since I am a current Calculus student, and will be taking Physics next semester. Anyways, I do have a question about one of my homework problems.

1. The problem statement, all variables and given/known data

Consider the function: f(x) = -2x^(3) + 6x^(2) - 3. Find its intercepts (there is more to this problem, but this is all I'm concerned about)

2. Relevant equations

I understand finding x intercepts requires setting the equation equal to 0, but that doesn't help me in this case.

3. The attempt at a solution

I've tried different things, from factoring to polynomial division, but I can't find the answer. Anyways, the answers are (-0.64, 0), (0.83, 0), and (2.81, 0). I just need help on how to find these intercepts.
Phys.Org News Partner Science news on
'Smart material' chin strap harvests energy from chewing
King Richard III died painfully on battlefield
Capturing ancient Maya sites from both a rat's and a 'bat's eye view'
Nov14-10, 08:41 PM
HW Helper
PF Gold
P: 2,841
Did you try Rational Roots Theorem? Your first listed expected answer at least appears that it would be found that way. You would then try to perform division of the function by the binomial obtained from use of Rational Roots Theorem, and you should have hopefully an easier quotient function to handle. You can always cheat and use a graphing calculator.
Nov15-10, 07:38 AM
Sci Advisor
PF Gold
P: 39,682
No, that has three real roots but none of them are rational. You will have to either use the Cardano's cubic formula,, or do a numerical calculation such as Newton's methods,'s_method

Register to reply

Related Discussions
Finding a tangent in a Cubic Function Calculus & Beyond Homework 7
Finding the equation of the line of a cubic function Calculus 5
Finding a cubic function Calculus & Beyond Homework 2
Finding a parabola given two x intercepts Precalculus Mathematics Homework 3
Finding cubic function Precalculus Mathematics Homework 3