Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Solving an equation after integrating

  1. Jun 30, 2011 #1
    1. The problem statement, all variables and given/known data

    i have an equation that i want to solve for b:
    [itex]\int _0^1 (a+b x)^2 x^c dx=2[/itex]

    2. Relevant equations
    \int _0^1 (a+b x)^2 x^c dx=2
    given: c>0

    3. The attempt at a solution

    To evaluate the integral on the left hand side, I expanded the bracket as:
    (a+b x)^2=a^2+2abx+(bx)^2.

    Then i evaluated the integral and simplifed the result to get:


    and now i'm stuck.
    Since we have linear and quadratic powers of b, i don't know how to make b the subject. any ideas will be very much appreciated.
    Thank you
  2. jcsd
  3. Jun 30, 2011 #2
    What is the integral


    Don't "simplify" anything, just calculate the integral, nothing more.
  4. Jun 30, 2011 #3
    after evaluating the integral, we have:

    (a^2/(c+1)) + (2ab/(c+3))+(b^2/(c+3))=2

    (this looks much cleaner :))

    but still, how would i make b the subject?

    thank you in advance
  5. Jun 30, 2011 #4
    Well, you have


    this is a quadratic equation in b and can be solved by the quadratic formula.
  6. Jun 30, 2011 #5
    so, i will have 2 solutions?
  7. Jun 30, 2011 #6
    Yes, unless the solutions coincide. But I doubt that will happen.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook