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# A Level maths help

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root 72 - root 27

Thank you xx
2. (Original post by M00ND4NC3R)

root 72 - root 27

Thank you xx
simplify both numbers
and then subtract
an example :
3. (Original post by fatima1998)
simplify both numbers
and then subtract
an example :
sorry, to help my understanding can you explain how to simplify the surd to root 12?
thanks x
4. (Original post by M00ND4NC3R)
sorry, to help my understanding can you explain how to simplify the surd to root 12?
thanks x
4 is the largest perfect square of 12
so you just need to find factors of number 4 x 3 = 12
there are others as well e.g.
12 x 1
6 x 2
but both of them cannot be squared but 4 can so you just find the factor of a number
5. (Original post by fatima1998)
4 is the largest perfect square of 12
so you just need to find factors of number 4 x 3 = 12
there are others as well e.g.
12 x 1
6 x 2
but both of them cannot be squared but 4 can so you just find the factor of a number
thanks but how did you get from root 72 down to root 12
6. Think of which square numbers go into both 72 and 27.

use 9 and split the surds remembering that
7. (Original post by M00ND4NC3R)
thanks but how did you get from root 72 down to root 12
first you need to find the factors of 72?
8. (Original post by fatima1998)
simplify both numbers
and then subtract
an example :
9. (Original post by fatima1998)
first you need to find the factors of 72?
I meant in your working when you initially showed me how to do it. The question was root 72 - root 27 but you started working out root 12 - root 27 so that was what confused me.

I have found many factors of 72 but none of them that i have found match the factors of 27 so that was why i was asking for help.
10. (Original post by NotNotBatman)
OMGGGG i wasn't answering the question, that question is completely separate (got that pic from google) - it was just an example for him to understand how to simplify

(Original post by M00ND4NC3R)
I meant in your working when you initially showed me how to do it. The question was root 72 - root 27 but you started working out root 12 - root 27 so that was what confused me.

I have found many factors of 72 but none of them that i have found match the factors of 27 so that was why i was asking for help.
so what are the factors of root 72?
11. (Original post by fatima1998)
OMGGGG i wasn't answering the question, that question is completely separate (got that pic from google) - it was just an example for him to understand how to simplify

Oh, my mistake.
12. (Original post by NotNotBatman)
Oh, my mistake.
nah its okay - well i didn't realise that the question also has root 27 in it but that was just a different example
13. (Original post by fatima1998)
OMGGGG i wasn't answering the question, that question is completely separate (got that pic from google) - it was just an example for him to understand how to simplify

so what are the factors of root 72?
72 can be written as
71 x 1
36 x 2
28 x 4
8 x 9
18 x 4

27 can be written as
27 x 1
3 x 9

I cant find any similarities
14. (Original post by M00ND4NC3R)
72 can be written as
71 x 1
36 x 2
28 x 4
8 x 9
18 x 4

27 can be written as
27 x 1
3 x 9

I cant find any similarities
okk so for 72 one
which factor is the biggest that can be squared as well
e.g. root 12
1 x12
2 x 6
3 x 4
the 4 can be squared because 2x2 = 4
so once you find the square number which is 2 (in this example) you just write it like it showed in an example
15. (Original post by fatima1998)
okk so for 72 one
which factor is the biggest that can be squared as well
e.g. root 12
1 x12
2 x 6
3 x 4
the 4 can be squared because 2x2 = 4
so once you find the square number which is 2 (in this example) you just write it like it showed in an example
I probably sound pathetic and useless and im sorry if im annoying you... ive worked out
for the 72 one
root 36x2 can be written as 6root2
root 28x4 can be written as 2root28
root 8x9 can be written as 3root8
root 18x4 can be ritten as 2root18

and for the 27 one
root 3x9 can be written as 3root3

however none of the numbers inside the root match to make it simple to answer.

I've only just started AS maths and struggled with surds at GCSE so this is why im so confused, im really sorry
16. (Original post by M00ND4NC3R)
I probably sound pathetic and useless and im sorry if im annoying you... ive worked out
for the 72 one
root 36x2 can be written as 6root2
root 28x4 can be written as 2root28
root 8x9 can be written as 3root8
root 18x4 can be ritten as 2root18

and for the 27 one
root 3x9 can be written as 3root3

however none of the numbers inside the root match to make it simple to answer.

I've only just started AS maths and struggled with surds at GCSE so this is why im so confused, im really sorry
you need to think which one is the largest
36 is the largest square number in that case
so we take 36x 2
so you take them and simplify 36 future 6x6 = 36
its okay i am also doing maths
17. (Original post by M00ND4NC3R)
..
Bah, all this with finding factors.

Here's a real easy way:

Of course, I could've just stopped at the second stage with root 36 if I recognised it as a square number. If not, just keep going until you get a square number you recognise.

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