Question

Quick question! How would I FOIL (3x + 7y)^2? I'm a little confused with the x's and y's...

Answer 1

you write it as (3x+7y)(3x+7y)
F first: 3x*3x = ?

Answer 2

3x^2?

Answer 3

remember, math people don't like to type
3x*3x is the same as 3*x*3*x
and when you multiply, you can change the order, so it could also be written 3*3*x*x
can you simplify it now?

Answer 4

so 9x^2?

Answer 5

yes
now O outer: 3x*7y (or for you, 3*x*7*y )

Answer 6

um 21xy? IS that even possible I don't know ):

Answer 7

yes, it is very possible x*y is xy (because xy means x*y)
now
I inner: 7y*3x (same thing as before)

Answer 8

21xy

Answer 9

and L last: 7y*7y

Answer 10

49y^2

Answer 11

Would I combine them to be 42x^2y^2?

Answer 12

so we have
9x^2 + 21xy + 21xy + 49y^2

the xy terms can be combined: if you factor out xy from
(21xy + 21xy)= (21+21)*xy= 42*xy or just 42xy

9x^2 +42xy + 49y^2

or you can say I have 21 xy's (whatever that is) and add 21 more xy's to get 42 xy's

Answer 13

Here is the idea for combining "like terms"
a "like term" has exactly the same letters (to the same power)
so x^2 matches x^2 but x^2 does NOT match x or x^3 (different powers)
and x does NOT match y
but xy matches yx (order does not matter)

so xy^2 matches xy^2 but not x^2y

Answer 14

If you want more info, maybe this helps
http://www.khanacademy.org/math/algebra/polynomials/v/multiplying-binomials

Answer 15

okay, so the answer would just be 3x^2 + 42xy + 49y^2?

Answer 16

I mean 9x^2****