已知(x-y+z)/y=(y-x+z)/x=(x+y-z)/z=k,求k的值还有一题在五边形ABCDE和五边形A'B'C'D'E'中,AB/A'B'=BC/B'C'=CD/C'D'=DE/D'E'=AE/A'E'=2/3，且五边形ABCDE的周长为68cm，求五边形A'B'C'D'E'的周长。

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