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alexeis_nicole

  • 3 years ago

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

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  1. sasogeek
    • 3 years ago
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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. King
    • 3 years ago
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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

  3. King
    • 3 years ago
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    understood? @alexeis_nicole

  4. alexeis_nicole
    • 3 years ago
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    yep.. i got 24 and 26... :S ?

  5. alexeis_nicole
    • 3 years ago
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    I MEAN ... 1.5 AND -1.75?

  6. agentx5
    • 3 years ago
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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).

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

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

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

  10. agentx5
    • 3 years ago
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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)

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

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

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

  14. agentx5
    • 3 years ago
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    You got it!

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

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

  17. alexeis_nicole
    • 3 years ago
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    uhm,.... lol

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