Difference between revisions of "2007 Cyprus MO/Lyceum/Problem 1"

Revision as of 15:15, 6 May 2007

If $x-y=1$ , then the value of the expression $K=x^2+x-2xy+y^2-y$ is

$\mathrm{(A) \ } 2\qquad \mathrm{(B) \ } -2\qquad \mathrm{(C) \ } 1\qquad \mathrm{(D) \ } -1\qquad \mathrm{(E) \ } 0$

$x^2+x-2xy+y^2-y=x^2-2xy+y^2+x-y=(x-y)^2+x-y=(1)^2+1=2\Longrightarrow\mathrm{ A}$

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 ==See also==
-*[[2007 Cyprus MO/Lyceum/Problems]]
+{{CYMO box|year=2007|l=Lyceum|before=First question|num-a=2}}
-*[[2007 Cyprus MO/Lyceum/Problem 2|Next Problem]]