The Purplemath Forums

by **buddy** on Fri Feb 27, 2009 5:44 pm

i have to simplify [sqrt(17)+sqrt(7)]*[sqrt(17)-sqrt(7)]

does that mean multiply it out? how do i do that?

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by **stapel_eliz** on Fri Feb 27, 2009 6:54 pm

buddy wrote:simplify [sqrt(17)+sqrt(7)]*[sqrt(17)-sqrt(7)]

Yes, you need to multiply this out. But it's a pretty simple thing to do, if you recognize that this is the factored form of a difference of squares.

. . . . . $a^2\, -\, b^2\, =\, (a\, +\, b)(a\, -\, b)$

Letting $a\, =\, \sqrt{17}$ and $b\, =\, \sqrt{7}$ , what do you get? :wink:

by **buddy** on Sat Feb 28, 2009 8:19 pm

17-7=10?

by **stapel_eliz** on Sat Feb 28, 2009 10:20 pm

buddy wrote:17-7=10?

Yup!

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simplify [sqrt(17)+sqrt(7)]*[sqrt(17)-sqrt(7)]

simplify [sqrt(17)+sqrt(7)]*[sqrt(17)-sqrt(7)]

Re: simplify [sqrt(17)+sqrt(7)]*[sqrt(17)-sqrt(7)]