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Weekly Problem 2 - 2013

Weekly Problem 2 -2013

Weekly Problem 39 - 2009

Stage: 2 and 3 Short Challenge Level: Challenge Level:1
$(1+x+y)^2-(1-x-y)^2=(1+2(x+y)+(x+y)^2)-(1-2(x+y)+(x+y)^2)=4(x+y)$.

This problem is taken from the UKMT Mathematical Challenges.

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