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28 November, 15:43

Factor completely 3x ^2 - 27

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  1. 28 November, 16:02
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    First, factor out a 3.

    3 (x² - 9)

    In any quadratic ax² + bx + c, we can split the bx term up into two new terms which we want to equal the product of a and c.

    In this case, we have x² + 0x - 9. (the 0x is a placeholder)

    We want two numbers that add to 0 and multiply to get - 9.

    Obviously, these numbers are 3 and - 3.

    Now we have 3 (x² + 3x - 3x - 9).

    Let's factor.

    3 (x (x+3) - 3 (x+3))

    3 (x-3) (x+3)

    There are multiple shortcuts which you could make here, FYI:

    Instead of splitting the middle, if your a value is 1, you can go straight to that step (x+number) (x+other number).

    Whenever you have a difference of squares, like a²-b², that factors to (a+b) (a-b).
  2. 28 November, 16:09
    0
    Both terms are multiply of 3, so you can factor 3 out;

    3 (x² - 9)

    Now, we can see that x² - 9 is difference of two perfect squares

    Recall that a² - b² = (a+b) (a-b)

    So we have x²-9 = (x+3) (x-3)

    So we can factor more here; 3 (x²-9) = 3 (x+3) (x-3)

    Final answer: 3 (x+3) (x-3)
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