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5√ 7 - 3√ 28

5√ 7 - 3√ 28

Bysteven

I have got stuck on the question 5√7 - 3√28.
I have looked at the solution and know that it is -√7 but I haven't managed to work out how to get there by working backwards from the answer.
Can someone please help me with a step by step method?
Cheers!

Reply 1

Old_Simon

What are the factors of 28 ?

Reply 2

mccrae01

factors of 28 are 7 and 4

So it is 5 root 7 minus (3 x root 7 x root 4)

As root 4 =2 we know it is 5 root 7 minus 6 root 7

This gives -1root 7 or just -root7.

Reply 3

Bysteven

Got it, thanks very much with your help :smile:

Quick Reply

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