i really need help with factoring....?

it's gonna be (x+5y)(x-4y)

first off, you wanna set up your sets :)

so... ( )( )

now you know that x won't have a number in front of it (if it does, you have to figure out what 2 numbers multiplied together equal that number)

so... (x )(x )

and since we're using the FOIL method (First, Outer, Inner, Last), we've already got the F part down. now we need to figure out the outer part. which will obviously be y.

so... (x y)(x y).

now we need to know if they need pluses or minuses. since the last term in the equation is -20y^2, you know that one needs a + and the other a -, because a + times a - equals a -.

so... (x+ y)(x- y)

now we need to figure out what two numbers multipled together will equal 20 and when added together will equal 1. that would be +5 and -4.

so...(x+5y)(x-4y).

and tah-dah!

to check...

(x+5y)(x-4y)

F: x*x= x^2

O: x*-4y= -4xy

I: x*5y= 5xy

L: 5y*-4y= -20y^2

put it all together: x^2-4xy+5xy-20y^2

reduce: x^2+xy-20y^2