Question

If one of the solutions to the cubic equation \( x^{3} + 4x^{2} + bx + c = 0 \) is \( -1 \), find values for b and c given that the polynomial has a double root.

Ask by Sullivan Hamilton. in South Africa
Jan 21,2025

Real Tutor Solution

Tutor-Verified Answer

Answer

The values are \( b = 5 \) and \( c = 2 \).

Solution

Sign in to Unlock Answers for Free!

A Learning Platform Trusted by Millions of Real Students and Teachers.

star-icon Unlock

Reviewed and approved by the UpStudy tutoring team

Bonus Knowledge

To determine the values of \( b \) and \( c \) in the cubic equation \( x^{3} + 4x^{2} + bx + c = 0 \) with a known double root and one root being \( -1 \), let’s denote the double root by \( r \). Therefore, the roots of the cubic can be \( -1, r, r \). Using Vieta's formulas, the sum of the roots gives us: \[ -1 + r + r = -4 \] which simplifies to: \[ 2r - 1 = -4 \implies 2r = -3 \implies r = -\frac{3}{2}. \] Now we have the roots \( -1, -\frac{3}{2}, -\frac{3}{2} \). Now we can express the cubic equation using its roots: \[ (x + 1)\left(x + \frac{3}{2}\right)\left(x + \frac{3}{2}\right) = 0. \] This can be expanded as follows: \[ (x + 1)(x + \frac{3}{2})^2 = (x + 1)\left(x^2 + 3x + \frac{9}{4}\right). \] Next, we multiply it out: \[ = x^3 + 3x^2 + \frac{9}{4}x + x^2 + 3x + \frac{9}{4} = x^3 + 4x^2 + \left(3 + \frac{9}{4}\right)x + \frac{9}{4}. \] Now we combine terms: \[ = x^3 + 4x^2 + \frac{21}{4}x + \frac{9}{4}. \] By comparison with the original polynomial \( x^{3} + 4x^{2} + bx + c = 0 \), we identify: \[ b = \frac{21}{4}, \quad c = \frac{9}{4}. \] Thus, the values of \( b \) and \( c \) are: \[ b = \frac{21}{4}, \quad c = \frac{9}{4}. \]

Latest Algebra Questions

Try Premium now!
Try Premium and ask Thoth AI unlimited math questions now!
Maybe later Go Premium
Study can be a real struggle
Why not UpStudy it?
Select your plan below
Premium

You can enjoy

Start now
  • Step-by-step explanations
  • 24/7 expert live tutors
  • Unlimited number of questions
  • No interruptions
  • Full access to Answer and Solution
  • Full Access to PDF Chat, UpStudy Chat, Browsing Chat
Basic

Totally free but limited

  • Limited Solution
Welcome to UpStudy!
Please sign in to continue the Thoth AI Chat journey
Continue with Email
Or continue with
By clicking “Sign in”, you agree to our Terms of Use & Privacy Policy