What is the factors for #x^2-x-20#?

Question

1574 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2018-03-24T20:52:31

#(x-5)(x+4)#

What factors of #-20# add up to the value of b which is #-1#?:
#4, -5#

#-4, 5#

#10, -2#

#-10, 2#

#20, -1#

#-20, 1#

It would be #4, -5#, therefore:
#(x-5)(x+4)#, since a is equal to 1

Answer 2 · 2018-03-24T20:54:15

#x^2-x-20 = (x+4)(x-5)#

#x^2-x-20#

In order to factor, we have to find factors of #-20# that when summed together give us #-1# (since #-1# is the coefficient of the middle term).

Factors of #-20#:
#(-1, 20),(1,-20),(2,-10),(-2, 10),(-4,5),color(blue)(((4,-5)))#

We see that #(4,-5)# has two factors for #-20# that when summed together equals #-1#.

So we can write our factor form:

#x^2-x-20 = (x+color(blue)(4))(xcolor(blue)(-5))#