(√a+√b)²=a+b+2√ab

determine the square root of 17+6√8

I hope you can help,

thanks.

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- Apr 4th 2008, 09:07 PMglenn101Surds...
(√a+√b)²=a+b+2√ab

determine the square root of 17+6√8

I hope you can help,

thanks. - Apr 4th 2008, 09:34 PMmr fantastic
A square root of a+b+2√ab is clearly √a+√b.

Note that 17 + 6√8 = 17 + 2√(9)(8) = 17 + 2√72.

Compare with a+b+2√ab.

Therefore solve the following two equations simultaneously:

a + b = 17 ... (1)

ab = 72 ... (2)

I get a = 9 and b = 8 (and obviously the other solution is a = 8 and b = 9) ......

Then a square root of 17+6√8 is √a+√b = ......