How do you factor the trinomial $a^2 - 4a - 21$ ?

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Answer 1 · 2016-03-30T15:15:24

$(a+3)(a-7)$

For a trinomial of this type we can factor it by looking for two numbers which multiply together to equal $-21$ and have a sum of $-3$

In this case: $(+3)$ and $(-7)$ meet tis requirement.

$(+3)(-7)=-21$

$(+3)+(-7)=-4$

Using this information I can factor $a^2-4a-21$ into:

$(a+3)(a-7)$

How do you factor the trinomial a^2 - 4a - 21a^2 - 4a - 21?