Question

Choose the correct product of (5x + 4)2.

25x2 + 40x + 16

25x2 − 16

25x2 + 16

25x2 − 40x + 16

Answer 1

(5x+4)(5x+4)

Do you know how to use the FOIL method?

Answer 2

no

Answer 3

First, Outer, Inner, Last.

Your first terms that you need to multiply are 5x and 5x
5x*5x = 25x^2

Your outer terms that you need to multiply are 5x and 4.
5x*4 = 20x

Your inner terms that you need to multiply are 5x and 4.
5x*4 = 20x

You last terms that you need to multiply are 4 and 4.
4*4 = 16

So you have 25x^2, 20x, 20x, and 16 that you need to "combine."

25x^2 +20x +20x +16

= 25x^2 +40x +16

Answer 4

ah wow thanks so much!

Answer 5

Watch this :-)

http://www.youtube.com/watch?v=Twtdsp0a1Iw

Answer 6

@phi
@CrazyMexican816

Answer 7

is this correct

Answer 8

i still dont nderstand @phi

Answer 9

yes

Answer 10

i dont know anything?

Answer 11

see Khan's vide if you have time
http://www.khanacademy.org/math/algebra/multiplying-factoring-expression/multiplying-binomials/v/multiplying-binomials

Answer 12

i know that \(\color{lime}{\huge\ (5x+4)^2~}\) = 25x^2+16 but i dont understand if i add a 40x

Answer 13

@phi ?

Answer 14

in FOIL i use 5x^2+4^2 but dont get why did they add a 40x?

Answer 15

do you know what you get when you multiply
a(x+y)

Answer 16

ax+ay?

Answer 17

yes.
now what if a was "complicated"
in other words, if a was short-hand for (c+d) ?
we would get
(c+d)x + (c+d)y

(I just replaced "a" with its equivalent (c+d) )

now we do the "distributive property" again:
(c+d)x is the same as x(c+d), or, xc +xd

and
(c+d)y is cy + dy

Answer 18

ohh

Answer 19

in other words
(c+d)(x+y) can be written as
xc + xd +yc +yd

we get FOUR terms (which would come from using FOIL, if you learn that)

Answer 20

foil is first out inner last

Answer 21

with
(5x+4)(5x+4)
we will get 4 terms, but we can combine two of the terms, and get 3 terms in the end

Answer 22

BTW i hope you dont ge confused cuz it looks like (5x + 4)•2 but it is (5x + 4)^2

Answer 23

let's use the distributive idea to do
(5x+4)(5x+4)
First, let a= (5x+4) so it's easier to see what we are doing:
a(5x+4)= a*5x +a*4

now replace a with (5x+4)
(5x+4)*5x + (5x+4)*4

now expand both terms:
can you do that ?

Answer 24

yes

Answer 25

5x(5x+4)+4(5x+4)
25x^2•20x+20x+16
ohhhhhh
thx @phi

Answer 26

the first part
5x(5x+4) is written as 25x^2 +20x
so you get all together
\[ 25x^2 +20x +20x +16\]

the last step is notice we have 20 x's plus 20 more x's which is 40 x's. we write
\[ 25x^2 +40x +16\]

Answer 27

hi