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# Surd Expansion??? watch

1. Hi help me dudes!

I am rather confused with the whole concept of GCSE mathematics, expanding brackets with Surds. For instance, one of the questions I find very difficult is:

Expand the brackets then and then simplify:

(√2-3)(√2+7)

Basically, I ca expand the expression but somehow cannot simlify it.

Please give me your thoughts into how I can resolve my problem with Surd Expansion.

Cheers
2. Show us what you got when you expanded it.
3. what have you got to?
4. ok when I expanded it I got √4√4 +7√2 -3√2 -21
5. just expand it as 2 normal brakets. so (a+b)(c+d)= ac+ad+bc+bd and then simplify by adding any of the terms which are numbers or surds of the same root together.
6. (Original post by PhyMath)
Show us what you got when you expanded it.

ok when I expanded it I got √4√4 +7√2 -3√2 -21

I used the "FOIL" method to expand
7. Where does come from?

Now collect like terms
8. (Original post by Danules)
just expand it as 2 normal brakets. so (a+b)(c+d)= ac+ad+bc+bd and then simplify by adding any of the terms which are numbers or surds of the same root together.
Ok thanks

So it would simlify into:

-17+5√2

???
9. (Original post by Sophie Maywood)
Ok thanks

So it would simlify into:

-17+5√2

???
No, be careful collecting terms
10. now you've expanded, simplify. so root 4 times root 4 is 4 as the root cancel out. 4-21= -17. 7lot of root 2 and - 3 lots of root 2 is like 7x-3x except x is root 2. so there are 4 root 2's. So simplified it is 4 lots of root2- 17.
11. What do you get when you times two of the same roots... Think about it.
12. So in theory, if you simplify a surd, then the number inside the root needs to be as small as possible and the number outside the surd needs to be the largest square number?

e.g

√48 = 4√3
13. √2 x √2 = 2

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