# expanding brackets

• Jan 18th 2010, 09:19 AM
andyboy179
multiplication
hi, i need to expand these brackets Attachment 14875, i know the answer will be 20 but i need to know what Attachment 14876=
• Jan 18th 2010, 09:22 AM
bigwave
Quote:

Originally Posted by andyboy179
hi, i need to expand these brackets Attachment 14875, i know the answer will be 20 but i need to know what Attachment 14876=

$(2-4\sqrt{3})(2+4\sqrt{3}) \Rightarrow 2^2 - (4\sqrt{3})^2 \Rightarrow 4-48 = -44$

$-2\times4\sqrt{3} = -8\sqrt{3}$

Edit:apparently I didn't go down the right path with this, as per definition of "expansion"
• Jan 18th 2010, 09:43 AM
andyboy179
at school we are told to work it out like this, (the blank spaces are the ones i don't know) Attachment 14878
• Jan 18th 2010, 09:44 AM
Wilmer
RULE: (x + y)(x - y) = x^2 - y^2

By the way, that's not "expanding brackets": it's a multiplication.
• Jan 18th 2010, 09:48 AM
Wilmer
Quote:

Originally Posted by andyboy179
at school we are told to work it out like this, (the blank spaces are the ones i don't know) Attachment 14878

BUT 4sqrt(3) times 4sqrt(3) = 48, not 24
• Jan 18th 2010, 09:54 AM
andyboy179
Quote:

Originally Posted by Wilmer
BUT 4sqrt(3) times 4sqrt(3) = 48, not 24

oh ye, i know what i did wrong! so what would -2 x 4sqrt(3)= ?
• Jan 18th 2010, 02:24 PM
Wilmer
Quote:

Originally Posted by andyboy179
oh ye, i know what i did wrong! so what would -2 x 4sqrt(3)= ?

Doesn't matter, because you also need to do +2 x 4sqrt(3), so the
2 will result in zero.
• Jan 18th 2010, 02:31 PM
VonNemo19
Quote:

Originally Posted by andyboy179
at school we are told to work it out like this, (the blank spaces are the ones i don't know) Attachment 14878

The method that you use in school, although correct, is not the method used by most (and when I say most-I mean almost all) institutions. A really good explaination of how these problems are done can be found here.

algebra.help -- Simplifying using the FOIL Method

BTW: Your method is not an "expansion" in the normal sense of the word, as someone has already mentioned. THe term expansion implies that there will be more terms after the mutiplication is complete (in most cases). And that thes terms may have likenesses.