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# Need help with surds core 1 watch

1. Ok so during summer holiday i forgot about surds. what is 2√7 x -2√7 and also can some explain how i would work out 4√9 x 3√7 thanks.
2. FIrst one multiply by the -2 then the second root 7. For the second one you multiply the exterior numbers by each other and the surds by each other.
3. (Original post by Student of ilm)
Ok so during summer holiday i forgot about surds. what is 2√7 x -2√7 and also can some explain how i would work out 4√9 x 3√7 thanks.
1. Squaring two identical square roots give the number of which they are the root. The rest is just multiplication.

2. Same as for 1. but remember the square roots of some numbers give nice answers.

Sorry, full solution had to go!
4. What happened to not posting full solutions to questions?

Here's a wiki site showing you the surd rules: https://en.wikibooks.org/wiki/A-leve...nd_Surds#Surds
5. so is 2√7x5 = 10√7 or √140
6. Not meant to give full solutions. With surds you are meant to go to the smallest surd number.
7. (Original post by Alex:)
What happened to not posting full solutions to questions?

Here's a wiki site showing you the surd rules: https://en.wikibooks.org/wiki/A-leve...nd_Surds#Surds
LOL, sorry, I didn't know that was a rule here. I'll edit my previous post now.
8. (Original post by Hydeman)
LOL, sorry, I didn't know that was a rule here. I'll edit my previous post now.
Alex already said that. My post was more for the OP as they were still asking for a full answer.
9. (Original post by Vikingninja)
Alex already said that. My post was more for the OP as they were still asking for a full answer.
Ah. Sorry about that. xD I'll un-quote you now.
10. (Original post by Hydeman)
1. Squaring two identical square roots give the number of which they are the root. The rest is just multiplication.

2. Same as for 1. but remember the square roots of some numbers give nice answers.

Sorry, full solution had to go!
Here :P

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