―、先化简,再求值:1:1/2x²-4(x²+1/3xy²)+2(1/6xy²-
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―、先化简,再求值:1:1/2x²-4(x²+1/3xy²)+2(1/6xy²-5/4x²),其中x=-2,y=-3;
2:已知,|m+n-2|+(mn+3)²=0,求2(m+n)-2[mn+(m+n)]+3[2(m+n)-3mn]的值.
2:已知,|m+n-2|+(mn+3)²=0,求2(m+n)-2[mn+(m+n)]+3[2(m+n)-3mn]的值.
1.
1/2x²-4(x²+1/3xy²)+2(1/6xy²-5/4x²)
=1/2x^2-4x^2-4/3xy^2+1/3xy^2-5/2x^2
=-6x^2-xy^2
=-6(-2)^2-(-2)*(-3)^2
=-6*4+2*9
=-24+18
=-6
2.
绝对值与平方数都是大于等于0的
两个大于等于的数相加,和为0
那么这两个数都等于0
m+n-2=0
mn+3=0
m+n=2
mn=-3
2(m+n)-2[mn+(m+n)]+3[2(m+n)-3mn]
=2*2-2(-3+2)+3[2*2-3*(-3)]
=4-2*(-1)+3(4+9)
=4+2+3*13
=6+39
=45
1/2x²-4(x²+1/3xy²)+2(1/6xy²-5/4x²)
=1/2x^2-4x^2-4/3xy^2+1/3xy^2-5/2x^2
=-6x^2-xy^2
=-6(-2)^2-(-2)*(-3)^2
=-6*4+2*9
=-24+18
=-6
2.
绝对值与平方数都是大于等于0的
两个大于等于的数相加,和为0
那么这两个数都等于0
m+n-2=0
mn+3=0
m+n=2
mn=-3
2(m+n)-2[mn+(m+n)]+3[2(m+n)-3mn]
=2*2-2(-3+2)+3[2*2-3*(-3)]
=4-2*(-1)+3(4+9)
=4+2+3*13
=6+39
=45
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