问题标题：
5道初一数学题,帮个忙1.已知x+y+z=5,且xy+xz+yz=5,求x²+y²+z²的值2.已知(x-3)²+(y+1)=0,求xy-4x²y²-(2xy²-3xy-xy²+4x²y²)-4xy的值3.(2x-5)+9(y+2)²=0,那么.4/5x-xy²+10=4.已知x=-
问题描述：
5道初一数学题,帮个忙
1.已知x+y+z=5,且xy+xz+yz=5,求x²+y²+z²的值
2.已知(x-3)²+(y+1)=0,求xy-4x²y²-(2xy²-3xy-xy²+4x²y²)-4xy的值
3.(2x-5)+9(y+2)²=0,那么.4/5x-xy²+10=
4.已知x=-2,y=1/10,z=1/2,求0.5x²y-[3/2x²y-3(xyz+2/3x²y)+yx²]-3xyz的值
5.12.5²-12.5+0.25
1.已知x+y+z=5,且xy+xz+yz=7,求x²+y²+z²的值
(刚才打错了)
要过程
彭建学回答：
1.因为(x+y+z)^2=x^2+y^2+z^2+2xy+2xz+2yz=5^2,所以x²+y²+z²=[(x+y+z)^2-2(xy+xz+yz)=25-2*7=25-14=11;2.题目应该是"已知(x-3)²+|y+1|=0,求xy-4x²y²-(2xy²-3xy-xy²+4x&sup...
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