Question

Solve by Factoring:
2a^2-a-21=0

Answer 1

@wolf1728

Answer 2

Doing the AC method, you take A times C, so 2 times -21 which equals -42. so what two numbers multiply to get -42 and add to get -1. 6 and -7 multiply to get -42 and add to get -1 so you use those two number to set up your equation.
y=(x+6)(x-7)
then set each part equation to 0.
0=x+6=-6
0=x-7=7
So the answer: x=-6 and x=7

Answer 3

2a^2-a-21=0
Divide by 2
a² -.5a -10.5
factors of -10.5 =
7 * 1.5
3 * 3.5

we need a negative third term and a negative second term so we change signs accordingly until we get:
(a + 3) • (a-3.5)

Answer 4

thanks... Do you know what What times what= 6 and add up to -2.5?

Answer 5

Hmm where are those numbers in the factoring?

Answer 6

Anyway -4 * -1.5 = 6
But do not add to -2.5

-4 * 1.5 = -6
and -4 + 1.5 = -2.5
Are you sure about the signs in that question?