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 May 17th, 2015, 09:19 AM #1 Senior Member   Joined: Nov 2013 Posts: 434 Thanks: 8 Permutations (a+b)P3=x and (a-b)P2=y find x+y
May 17th, 2015, 11:43 AM   #2
Math Team

Joined: Dec 2006
From: Lexington, MA

Posts: 3,267
Thanks: 408

Hello, mared!

Quote:
 $_{a+b}P_{_3} \:=\: x$ $_{a-b}P_{_2} \:=\: y$ $\text{Find }\,x\,+\,y$

$x\;=\;(a+b)(a+b-1)(a+b-2)$
$y \;=\;(a-b)(a-b-1)$

$\text{Therefore: }\:x\,+\,y \;=\;(a+b)(a+b-1)(a+b-2)\,+\,(a-b)(a-b-1)$

I'll let you simplify it.

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