How do you factor $a^2-a-90$ ?

Question

3554 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-05-21T18:59:11

You find the roots and turn them into factors:

(Using Bhaskara here)

$(1+-sqrt(1-4(1)(90)))/2$
$(1+-19)/2$
Roots:
$a=10$ , which can be rewritten as $(a-10)=0$
$a=-9$ , which can be rewritten as $(a+9)=0$

Thus, $a^2-a-90=(a-10)(a+9)$

Answer 2 · 2015-05-21T21:01:53

A different method.

Problem: Factor $a^2-a-90$ .

Find two numbers that when added equal -1, and when multiplied equal -90.

The numbers -10 and 9 fit the criteria.

$a^2-a-90=(a+9)(a-10)$

How do you factor a^2-a-90a^2-a-90?