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alexeis_nicole Group Title

how would i factor 8x^2 + 2x -21

  • 2 years ago
  • 2 years ago

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  1. sasogeek Group Title
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    multiply the coefficient of the x^2 term by the constant and find 2 factors of the result that when you add or subtract will give you the x coefficient, replace the x coefficient with the two factors in a way that when you subtract or add them, you'll get the x coefficient. you'll get 4 terms. take the first two terms and factor them, take the last two terms and factor them. you're done. if you didn't understand what i've just written, read it carefully again, take your time, and solve it.

    • 2 years ago
  2. King Group Title
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    You can use the quadratic equation formula (-b +or-sqrt(b^2-4ac))/2a here a,b,c are the coefficients ax^2+bx+c

    • 2 years ago
  3. King Group Title
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    understood? @alexeis_nicole

    • 2 years ago
  4. alexeis_nicole Group Title
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    yep.. i got 24 and 26... :S ?

    • 2 years ago
  5. alexeis_nicole Group Title
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    I MEAN ... 1.5 AND -1.75?

    • 2 years ago
  6. agentx5 Group Title
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    Quadratic Formula in an easier-to-read form: \[x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}\] Binomials will be written as (where a, b, and c are numerical constants) \[ax^2 + bx + c\] You can always check your factorization by multiplying it back together to get the original expanded form (what you have initially here).

    • 2 years ago
  7. agentx5 Group Title
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    1.5 and -1.75 are correct, but put them in fraction form and you'll have a huge hint ;-)

    • 2 years ago
  8. alexeis_nicole Group Title
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    3/2 and -7/4 ?

    • 2 years ago
  9. agentx5 Group Title
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    Huge hint: \[\frac {numerator}{demominator} = \frac {c}{a}\]

    • 2 years ago
  10. agentx5 Group Title
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    (ax+c)(ax+c) (but different a's and c's, call them a1 & c1 and a2 & c2 if you want)

    • 2 years ago
  11. agentx5 Group Title
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    Here's one of the two, so you're not getting confused: -7/4 --> (4x+7)

    • 2 years ago
  12. agentx5 Group Title
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    Here's how to check, solve this: \[4x+7 = 0 \]

    • 2 years ago
  13. alexeis_nicole Group Title
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    OH !!!!! (2x-3) (4x+7)

    • 2 years ago
  14. agentx5 Group Title
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    You got it!

    • 2 years ago
  15. agentx5 Group Title
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    Do you see why the -/+ sign switches?

    • 2 years ago
  16. agentx5 Group Title
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    So here's the next step they'll probably introduce you to later, they'll ask you to solve this: \[8x^2 + 2x -21 = (2x-3)(4x+7) = 0\]

    • 2 years ago
  17. alexeis_nicole Group Title
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    uhm,.... lol

    • 2 years ago
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