Factor the quadratic expression:
4x^2-11x-20..
Can someone walk me through this?

Question

Factor the quadratic expression: 
4x^2-11x-20..
Can someone walk me through this?

amistre64 · Answer

IF it factors into rationals ... then you can do a process such that the factors of ac sum to b

anonymous · Answer

I'm not sure how to do that though is the problem.

amistre64 · Answer

what is 4*-20?

anonymous · Answer

-80

amistre64 · Answer

what are all the factors of -80?

anonymous · Answer

1   80
2   40 
4   20
5   16
8   10

amistre64 · Answer

1,80
2,40
4,20
8,10
16,5 ... this one seems promising

-16+5 = -11, right?

anonymous · Answer

Correct.

amistre64 · Answer

so,  lets set it up ... 

(x-16) (x+5)

since we multiplied by 4 to find it, we should really divide it back out so...

(x -16/4) (x+5/4);  reduce the fractions, if theres anything left on the bottom, stick it back in front where we got it from

anonymous · Answer

So wouldn't it end up being 4(x-16)(x+5)?

amistre64 · Answer

hmm, not quite

16/4 = 4
5/4  is not reducing, so stick the 4 back in front to get

(x-4) (4x+5)

anonymous · Answer

Ohh! Okay I get it!

amistre64 · Answer

IF this process doesnt work out ... then we have some sqrts of irrationals that come about.

anonymous · Answer

Thank you so much for your help!

amistre64 · Answer

good luck