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Math Help - Multiplying Binomials Quickly

  1. #1
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    Multiplying Binomials Quickly

    Example 2
    Using FOIL to find a product quickly
    Find each product. Write down only the answer.
    a) (x + 3)(x + 4)
    a) (x + 3)(x + 4) = x2 + 7x + 12 Combine like terms: 3x + 4x = 7x.
    I don't understand this. I get how they got 3x+4x=7x but i do not understand how that is equal to x2 + 7x + 12?

    Using foil you get x2 + 7x + 12 if you combine like terms you get 3x + 4x = 7x I can't wrap my head around why these are equivelent statements.
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  2. #2
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    Quote Originally Posted by pkraus View Post
    Example 2
    Using FOIL to find a product quickly
    Find each product. Write down only the answer.
    a) (x + 3)(x + 4)
    a) (x + 3)(x + 4) = x2 + 7x + 12 Combine like terms: 3x + 4x = 7x.
    I don't understand this. I get how they got 3x+4x=7x but i do not understand how that is equal to x2 + 7x + 12?

    Using foil you get x2 + 7x + 12 if you combine like terms you get 3x + 4x = 7x I can't wrap my head around why these are equivelent statements.
    x^2+4x+3x+12 is the same as x^2+7x+12

    I hope this is what you were asking for!
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  3. #3
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    I understand that what i don't understand is why ..

    x^2 + 7x + 12

    equal to

    3x + 4x = 7x
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  4. #4
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    Quote Originally Posted by pkraus View Post
    I understand that what i don't understand is why ..

    x^2 + 7x + 12

    equal to

    3x + 4x = 7x
    They are not saying this at all. They are simply saying that when you expand, the terms you get include 3x + 4x. These terms are added to give 7x. It's as simple as that. They are simply explaining where the 7x has come from.
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  5. #5
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    FOIL (x+ 3)(x+ 4)

    F ("First times First"): x*x= x^2
    O ("Outside times Outside"): x*4= 4x
    I ("Inside times Inside"): 3*x= 3x
    L ("last times Last"): 3*4= 12

    Now add ALL of those: x^2+ 4x+ 3x+ 12= x^2+ 7x+ 12

    "FOIL" involves 4 parts "4x+ 3x= 7x" is only two of those.
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