{x+y=22 x+z=-27 y+z=13
(x+y-z)(x-y+z)=
X+Y+Z=?
解方程组{x+y=22,y+z=13,z+x=-27
f(x,y,z,w)=x*(x+y)*(x+y+z)*(x+y+z+w)
设X,Y,Z都是整数,满足条件(X-Y)(Y-Z)(Z-X)=X+Y+Z,试证明X+Y+Z能被27整除
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