...3xy^2-5xy^2，其中x=1，y=-1jjjjjjjjjjjjjjjjjj...

精选知识

2x^2y+4x^2y-3xy^2-5xy^2

=6x^2y-8xy^2

=6×1^2×(-1)-8×1×(-1)^2

=-6-8

=-14

其他类似问题

问题1：先化简再求值:1.4x的平方+3xy-x的平方-3xy+9,其中x=-2 2.3-[3（x+2y）-2（x-1）],其中x=-1,y=-三分之一[数学科目]

4x的平方+3xy-x的平方-3xy+9

=4x的平方-x的平方+3xy-3xy+9

=3x的平方+9

=3*(-2)的平方+9

=3*4+9

=12+9

=21

3-[3（x+2y）-2（x-1）]

=3-(3x+6y-2x+2)

=3-3x-6y+2x-2

=3-2-3x+2x-6y

=1-x-6y

=1-(-1)-6*(-1/3)

=1+1+2

=4

问题2：先化简再求值：设：A=2x^2-3xy+y^2-x+2y B=4x^2-6xy+2y^2-3x-y ,若/x-2a/+(y+3)^2=0,且B-2A=a;求A的[数学科目]

a=B-2A=(4x²-6xy+2y²-3x-y)-2*(2x²-3xy+y²-x+2y)

=4x²-6xy+2y²-3x-y-4x²+6xy-2y²+2x-4y

=-x-5y

因为/x-2a/+(y+3)²=0

所以 (y+3)²=0 解得y=-3

/x-2a/=0

/x-2(-x-5y)/=/x+2x+10y/=/3x+10y/=/3x+10*(-3)/=/3x-30/=0

解得x=10

A=2x²-3xy+y²-x+2y=(x-y)(2x-y)-x+2y=13*23-10-6=283

B=4x²-6xy+2y²-3x-y=2(2x²-3xy+y²)-3x-y=2*13*23-30+3=571

问题3：化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy][数学科目]

3x^2-[5xy-(x^2y-3xy)+4x^2y-8xy]

= 3x^2-[5xy-x^2y+3xy+4x^2y-8xy]

= 3x^2-5xy+x^2y-3xy-4x^2y+8xy

= 3x^2-3x^2y

= 3x^2 (1 - y)

问题4：先化简再求值：设：A=2x^2-3xy+y^2-x+2y B=4x^2-6xy+2y^2-3x-y ,若/x-3a/+(y+5)^2=0,且B-2A=a;求A的[数学科目]

∵|x-3a|≥0,(y+5)^2≥0

又：|x-3a|+(y+5)^2=0

∴|x-3a|=(y+5)^2=0

∴x=3a,y=-5

a=B-2A= 4x^2-6xy+2y^2-3x-y -2(2x^2-3xy+y^2-x+2y )

= 4x^2-6xy+2y^2-3x-y -4x^2+6xy-2y^2+2x-4y

= -x-5y

x=3a=-3x-15y

x=-15y/2=-15*(-5)/2=75/2

A = 2x^2-3xy+y^2-x+2y

= (2x-y)(x-y)-x+2y

= （75+5)(75/2+5)-75/2+2*(-5)

= 80*85/2 - 75/2-10

= 340-38+1/2-10

= 292又1/2

问题5：(3/2x^2-5xy+y^2)-[-3xy+2(1/4x^2-xy)+2/3y^2],其中x=1,y=-2 化简求值[数学科目]

(2分之3x的2次方-5xy+y的2次方)-【-3xy+2(4分之一x的2次方-xy)+3分之2y的2次方】

=3/2x2-5xy+y2-(-3xy+1/2x2-2xy+2/3y2)

=3/2x2-5xy+y2+5xy-1/2x2-2/3y2

=x2-1/3y2