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Factor completely. z^5 - 4z^4 - 21z^3

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schooledmom | Salutatorian

Posted August 12, 2013 at 5:05 PM via web

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Factor completely.

z^5 - 4z^4 - 21z^3

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samhouston | Middle School Teacher | (Level 1) Associate Educator

Posted August 12, 2013 at 5:11 PM (Answer #1)

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z^5 - 4z^4 - 21z^3

First, factor out z^3.
z^3(z^2 - 4z - 21)

Next, find two numbers whose product is -21 and sum is -4.
-7 * 3 = -21
-7 + 3 = -4

Now use these numbers to factor the trinomial.
z^3(z - 7)(z + 3)

Final answer:
z^3(z - 7)(z + 3)

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