Question

Factor completely: 10x2 + 2x − 8

Answer 1

can you see how to start ?. Is there a common factor in all 3 terms ?

Answer 2

the choices are:

2(5x − 1)(x + 4)

2(5x − 4)(x + 1)

2(5x + 2)(x − 2)

2(5x − 2)(x + 2)

Answer 3

it is 2.

Answer 4

then it looks like
5x^2 + x - 4

Answer 5

is it the third one?

2(5x + 2)(x − 2)?

Answer 6

sorry - I got distracted...

Answer 7

its ok

Answer 8

yes or no please... :/

Answer 9

when I have to factor a quadratic like that I do it mostly by trial and error (I don't remember the cross multiply thing)
You know that one term must start with 5x, so
(5x + a?)(x - b?)
since you 5x*b (+-) a?*x = 1, then obviously b cannot 4, so you have
(5x +(-)4)(x +(-)b?)
now you know 4 * b = 4, so b - 1.
Now it is a matter finding the correct signed for (+)(-).

Sorry - that was probably not very helpful, but those are the steps I usually do when factoring. If I get really stuck I use the quadratic formula as a last resort.

Answer 10

try distribute
(5x + 2)(x − 2)
= 5x^2 - 10x + 2x - 4
= 5x^2 - 8x - 4
so that is not the answer

Answer 11

ok then you just switch the signs. is it the last one?

Answer 12

try distribute
(5x − 2)(x + 2)
5x^2 + 10x - 2x - 4
5x^2 + 8x - 4
so no :)

Answer 13

but then you have to multiply the 5x by 2

Answer 14

2(5x^2 + x - 4)
so ignore the 2 for now and look for something where
(5x +- A)(x +- B) = 5x^2 + x - 4

so 5x(B) - A(x) = 1, (1x)
and (A)(B) = -4

Answer 15

I'm not really good at explaining this - sorry about that.

Answer 16

can you tell me what one it is? I am totally confused...

Answer 17

2(5x-4)(x+1)
= 2(5x^2 + 5x - 4x - 4)
= 2(5x^2 + 1x - 4)
= 10x^2 + 2x - 8

Answer 18

you see that?

Answer 19

ok