Help with "expand and simplify expression" question please

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devonmum
Posts: 33
Joined: Sun Oct 23, 2011 4:55 am

Help with "expand and simplify expression" question please

Post by devonmum »

Hello

Could somebody tell me how to work out the following please?

(2j - 7k) (3j + 4k)


Thanks
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: Help with "expand and simplify expression" question plea

Post by Guest55 »

(2j - 7k) (3j + 4k) is not 11+ stuff

(2j - 7k) (3j + 4k) = 2j (3j + 4k) -7k (3j + 4k) etc

can't write it out properly as no superscripts
devonmum
Posts: 33
Joined: Sun Oct 23, 2011 4:55 am

Re: Help with "expand and simplify expression" question plea

Post by devonmum »

Thank you for your help with that, makes sense now! Been trying that for ages..... :roll:
Paramjeet
Posts: 228
Joined: Sun Mar 18, 2012 6:30 pm

Re: Help with "expand and simplify expression" question plea

Post by Paramjeet »

(a-b)(c-d)= ac-bc-ad+bd

Watch out for the change in signage though...2 minuses becoming a plus

This is Year 7 algebra, not 11+ entrance standard
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: Help with "expand and simplify expression" question plea

Post by Guest55 »

Paramjeet - it is not a good idea to say 'two minuses make a plus' because that gives problems when you calculate - 5 - 8 and children think the answer is + 13!
Paramjeet
Posts: 228
Joined: Sun Mar 18, 2012 6:30 pm

Re: Help with "expand and simplify expression" question plea

Post by Paramjeet »

hi, yep your right as always.

I teach my child that when you have 2 minues, you add and put the sign of the minus. In the example quoted, it did not warrant it.
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