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 September 12th, 2019, 05:30 AM #1 Senior Member   Joined: Dec 2015 From: somewhere Posts: 642 Thanks: 91 Evaluate expression if $\displaystyle n^2 -n =2 \:$ , find $\displaystyle n^2 +n\;$, $\displaystyle n\in \mathbb{N}.$ September 12th, 2019, 09:21 AM   #2
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Quote:
 Originally Posted by idontknow if $\displaystyle n^2 -n =2 \:$ , find $\displaystyle n^2 +n\;$, $\displaystyle n\in \mathbb{N}.$
$\displaystyle n^2 - n = 2$
$\displaystyle n^2 + n = f(n)$
where f(n) is, so far, an undetermined function.

Subtract these:
$\displaystyle -2n = 2 - f(n)$

$\displaystyle f(n) = 2n + 2$

So...
$\displaystyle n^2 + n = 2n + 2$

Is this what you were looking for? (And yes, there is probably a better way to do this.)

-Dan September 12th, 2019, 09:26 AM #3 Math Team   Joined: Jul 2011 From: Texas Posts: 3,016 Thanks: 1600 $n^2-n = 2 \implies (n-2)(n+1) = 0 \implies n = 2 \in \mathbb{N} \implies n^2+n = 6$ ... or am I missing something? Thanks from topsquark, idontknow and DarnItJimImAnEngineer September 12th, 2019, 10:24 AM #4 Senior Member   Joined: Jun 2019 From: USA Posts: 213 Thanks: 90 I agree. n(n-1) = 2 -> n = 2, 2^2+2 = 6. Thanks from topsquark and idontknow Tags evaluate, expression Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post Shamieh Calculus 16 November 19th, 2013 06:44 PM kingkos Algebra 9 October 2nd, 2012 09:33 AM Riazy Algebra 3 September 1st, 2011 01:32 PM kev085 Algebra 1 April 24th, 2009 04:06 AM woodman5k Algebra 2 October 10th, 2007 04:53 PM

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