Results 1 to 4 of 4

Math Help - is this a way to solve a radical equation?

  1. #1
    Junior Member
    Joined
    Mar 2011
    Posts
    25

    is this a way to solve a radical equation?

    (2x^2-7)^(1/2)=3-x

    so FOIL the left side, square the right side for, 2x^2-7=x^2-6x+9. Add 7: 2x^2=x^2-6x+16 but then divide by 2 instead of adding 2x^2: x^2=(x^2-6x+16)(1/2).
    Then subtract x^2 and get .5x^2-3x+8=0. Then use the quadratic formula to solve for x.

    Is this a licit way to solve this? If not, then why not?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,487
    Thanks
    1391
    No. You can't FOIL the left hand side because it's not the product of two binomials...

    What you actually have is Sqrt(2x^2 - 7) = 3 - x.

    Start by squaring both sides to undo the square root, then expand the RHS and solve the resulting quadratic.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Mar 2011
    Posts
    25
    Quote Originally Posted by Prove It View Post
    No. You can't FOIL the left hand side because it's not the product of two binomials...

    What you actually have is Sqrt(2x^2 - 7) = 3 - x.

    Start by squaring both sides to undo the square root, then expand the RHS and solve the resulting quadratic.
    Don't you have to foil the left side then, since you are squaring both sides? That's what I meant in any case.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,886
    Thanks
    325
    Awards
    1
    Quote Originally Posted by bournouli View Post
    Don't you have to foil the left side then, since you are squaring both sides? That's what I meant in any case.
    You do not FOIL the LHS. That is what Prove It is trying to say.
    sqrt(2x^2 - 7) = 3 - x

    [ sqrt(2x^2 - 7) ]^2 = (3 - x)^2

    2x^2 - 7 = (3 - x)^2

    Now FOIL the RHS... Also, when you are done check your solutions to make sure they work. Squaring both sides of an equation often introduces extra solutions.

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. should be easy to solve for x radical
    Posted in the Algebra Forum
    Replies: 1
    Last Post: March 2nd 2010, 01:52 PM
  2. Solve the radical equation
    Posted in the Algebra Forum
    Replies: 4
    Last Post: February 8th 2010, 02:13 PM
  3. Solve this radical equation
    Posted in the Algebra Forum
    Replies: 5
    Last Post: September 22nd 2009, 09:38 PM
  4. Radical-Radical equation
    Posted in the Algebra Forum
    Replies: 6
    Last Post: June 27th 2009, 03:38 AM
  5. solve radical expression
    Posted in the Algebra Forum
    Replies: 7
    Last Post: March 16th 2008, 07:39 PM

Search Tags


/mathhelpforum @mathhelpforum