Question

please help;
factor: 6x^2+xy-40y^2

Answer 1

k so your going to end up with something close to:
( x + y ) ( x - y ), yeah?

Answer 2

now is we use FOIL
we know that the x time the x has to equal 6x^2
so factors of 6 are 1,6 and 2,3

Answer 3

we also know that the y's will multiply out to -40 (hence the + and the - in our brackets)
so factors of 40 are 1,40 2,20 4,10 5,8

Answer 4

now, the x multipliers have to add up to 1xy...
so which of the above factor combinations fits the bill here?

Answer 5

2,3?

Answer 6

spot on dude
(3x +8y) (2x -5y)
= 6x^2 -15xy + 16xy -40y^2

Answer 7

oo because you group at the end?

Answer 8

yup so the -15 and the plus 16 yo can add because they're like terms, so they become a +1

Answer 9

but doesnt the c multiples also have to add up to b?

Answer 10

yes but the sum of the c (times the a multiples) equal the b multiples

Answer 11

a = first x first
c = last x last
b = sum of inners multiplied + and outers multiplied

Answer 12

alright thanks man

Answer 13

always welcome dude