计算①(2x+y-3z)²；②y（x+y)+(x-y)²-x²-2y².

来源：学生作业帮编辑：作业帮分类：综合作业时间：2024/06/05 23:58:26

①(2x+y-3z)²
=(2x+y)²-6z(2x+y)+9z²
=4x²+4xy+y²-12xz-6yz+9z²
②y（x+y)+(x-y)²-x²-2y²
=xy+y²+x²-2xy+y²-x²-2y²
=-xy
再问： 1.��|x+y-5|+(xy-6)²=0��x²+y²��ֵ�� 2.��֪��m-n)²=8��m+n��²=2��m²+n²=
再答： 1、x+y-5=0 xy=6 ∴x+y=5 x²+y²=(x+y)²-2xy=5²-12=13 2、由(1)得 m²-2mn+n²=8 (3) 由(2)得 m²+2mn+n²=2 (4) (3)+(4)得 2m²+2n²=10 ∴m²+n²=5

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