Results 1 to 5 of 5

Math Help - Algebra II: Complex Numbers & Trinomials & Factoring

  1. #1
    Newbie
    Joined
    Nov 2008
    Posts
    3

    Algebra II: Complex Numbers & Trinomials & Factoring

    I need help with these problems please:
    Solve by Factoring:
    3x^2 + 6x - 24 = 0
    The problem i got is that any combination of number I got that produced -24 didn't add to 6.

    And:

    5x^2 - 40x - 45 = 0

    And:

    9x^2 + 24x + 16

    Solve the equation.
    4x^2 + 9 = 0
    The answers were:
    a. \frac{-3}{2}i, \frac{3}{2}i b. \frac{-9}{4}i , \frac{9}{4}i

    Use the Quadratic Formula to solve the equation.
    -2x^2 - 5x + 3 = 0
    My solution didn't match the 2 possible answers provided:
    \frac{-27}{2} , 11 and -3 , \frac{1}{2}

    4x^2 - x + 9 = 0
    provided possible answers:
    \frac{1}{4} +- \frac{i\sqrt143}{4} or \frac{1}{8} +- \frac{i\sqrt143}{8}

    I know its kind of alot but I absolutely cannot figure this out! Help is very appreciated
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Drew_445 View Post
    I need help with these problems please:
    Solve by Factoring:
    3x^2 + 6x - 24 = 0
    The problem i got is that any combination of number I got that produced -24 didn't add to 6.

    Mr F says: Start by writing it as 3(x^2 + 2x - 8) = 0.

    And:

    5x^2 - 40x - 45 = 0

    Mr F says: Start by writing it as 5(x^2 - 8x - 9) = 0.

    And:

    9x^2 + 24x + 16

    Mr F says: This has the form of a perfect square.

    Solve the equation.
    4x^2 + 9 = 0

    Mr F says: {\color{red}x^2 = -\frac{9}{4} \Rightarrow x = \sqrt{-\frac{9}{4}} = \pm i \, \frac{3}{2}}.

    The answers were:
    a. \frac{-3}{2}i, \frac{3}{2}i b. \frac{-9}{4}i , \frac{9}{4}i

    Use the Quadratic Formula to solve the equation.
    -2x^2 - 5x + 3 = 0
    My solution didn't match the 2 possible answers provided:
    \frac{-27}{2} , 11 and -3 , \frac{1}{2}

    Mr F says: Show your working.

    4x^2 - x + 9 = 0
    provided possible answers:
    \frac{1}{4} +- \frac{i\sqrt143}{4} or \frac{1}{8} +- \frac{i\sqrt143}{8}

    Mr F says: Show your working.

    I know its kind of alot but I absolutely cannot figure this out! Help is very appreciated
    ..
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Nov 2008
    Posts
    3
    Use the Quadratic Formula to solve the equation.


    Mr F says: Show your working.

    x = \frac{5 +- \sqrt25-4(-2)(3)}{-4}

    \frac{5 +- \sqrt1}{-4}
    So the solution I got was +-5 over 4, which doesn't answer any of the possible answers.

    So what do i do?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Drew_445 View Post
    Use the Quadratic Formula to solve the equation.


    Mr F says: Show your working.

    x = \frac{5 +- \sqrt25-4(-2)(3)}{-4} Mr F says: Correct.

    \frac{5 +- \sqrt1}{-4} Mr F says: Wrong.

    So the solution I got was +-5 over 4, which doesn't answer any of the possible answers.

    So what do i do?
    x = \frac{5 \pm \sqrt{25 - 4(-2)(3)}}{-4} = \frac{5 \pm \sqrt{25 {\color{red}+} 24}}{-4} = \frac{5 \pm 7}{-4} = -3, ~ \frac{3}{4}.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Nov 2008
    Posts
    3
    oh wow such a simple solution

    thanks very much
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Factoring z^4+1 over the complex numbers
    Posted in the Pre-Calculus Forum
    Replies: 8
    Last Post: March 1st 2011, 03:09 AM
  2. factoring with complex numbers
    Posted in the Algebra Forum
    Replies: 3
    Last Post: September 13th 2009, 08:12 AM
  3. factoring trinomials?
    Posted in the Algebra Forum
    Replies: 11
    Last Post: April 17th 2008, 09:55 PM
  4. Replies: 3
    Last Post: November 6th 2006, 12:02 AM
  5. Factoring Trinomials ....
    Posted in the Algebra Forum
    Replies: 3
    Last Post: May 1st 2006, 07:51 PM

Search Tags


/mathhelpforum @mathhelpforum