有理数x,y,z
|x-z-2|+|3x-6y-7|+(3y+3z-4)的平方=0
|x-z-2|>>0,|3x-6y-7|>>0,(3y+3z-4)的平方>>0
x-z-2=0,
|3x-6y-7=0,
3y+3z-4=0
解方程组：x=3,y=1/3,z=1
x的3n次方y的3n-1次方z的3n+1次方-x
=3^3n*(1/3)^(3n-1)*1^(3n+1)-3
=3^3n*3^(1-3n)*1-3
=3^3n*3/3^3n-3
=3-3
=0