Question

http://oi41.tinypic.com/308flw8.jpg Could someone please explain the highlighted part? Their explanation just confused me even more.

Answer 1

your leading coefficient if 5
if you have any hope of factoring it has to be
\[(5y+whatever)(y+yada)\]

Answer 2

otherwise you will never get \(5y^2\)

Answer 3

now you have to think of two numbers whose product is -12
you have lots of choices

Answer 4

@satellite73 How does the 5 change which numbers I'm going to plug in for whatever and yada?

Answer 5

i suck at factoring, but one thing is clear, one number has to be positive, the other negative, because otherwise you are not going to get \(-12\) so we can try something, say
\[(5y-2)(y+6)\] and see what happens

Answer 6

you would get
\[5y^2+30y-2y-12\] which is clearly wrong, because the middle term is supposed to be \(4y\) and it isn't

Answer 7

really it is a matter of trial and error, for the most part

Answer 8

\((5y+3)(y-4)=5y^2-20y+3y-12\) nope

Answer 9

Oh! It's\[(5y-6)(y+2)\]

Answer 10

yes

Answer 11

Thanks :) You were really helpful!

Answer 12

we could try to be a bit more systematic, by saying \(ab=-12, a+5b=4\) but it is not too clear how to solve that either

Answer 13

yw