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A Cry for Help

  1. Oct 12, 2006 #1
    I might not be the brightest bob in the bunch but I am having trouble with a simple quadratic equation.

    k^2 + (k + 4)^2 = 346

    According to my manual expands to:

    k^2 + k^2 + 8k + 16 = 346

    Everything is going fine until I see the 8k. Where did the 8k come from? Or is my manual wrong?

    If anyone is willing to aid a poor soul with his maths I would be very grateful.
     
  2. jcsd
  3. Oct 12, 2006 #2
    Hmm...

    [tex] k^2 + (k+4)^2 = 346 [/tex]

    When you square k+4, please remember that it is not [tex] k^2 + 16 [/tex], but rather [tex] (k+4)(k+4) [/tex], which is a polynomial. After you finish using the FOIL method, you get [tex] k^2 + 4k + 4k + 16 [/tex], which can be simplified to [tex] k^2 + 8k + 16 [/tex], which is how you get your 8k.

    The solution to the problem is 11 :smile: (Quadratic Equation).

    Besides... are you in 9th grade?
     
  4. Oct 12, 2006 #3
    yes

    Because (k + 4) ^2 = (k+4)(k+4) and you cant just multiply k*k and add it to 4*4 you have to multiply each element as in: k*k + k*4 + k*4 +4*4 which will give you k^2 + 8k + 16. so if you had (k+ 3)(k + 2) = k^2 + 2*k + 3*k + 6
     
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