大师作文网已知A=x^2-xy-y^2,B=3xy+x^2.x,y满足条件(x-3)^2+(y+2)^2=0求1/2[2(A-B)
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已知A=x^2-xy-y^2,B=3xy+x^2.x,y满足条件(x-3)^2+(y+2)^2=0求1/2[2(A-B)-3A+1/3[3（A+2B）-3A]-1/2A
完整
完整
(x-3)^2+(y+2)^2=0
(x-3)^2=0,(y+2)^2=0
x=3
y=-2
1/2[2(A-B)-3A+1/3[3（A+2B）-3A]-1/2A
=1/2[(A-B)-3A+A+2B-3A]-1/2A
=1/2[A-B-3A+A+2B-3A]-1/2A
=1/2[A-3A+A-3A-B+2B]-1/2A
=1/2[-4a+B]-1/2A
=-2A+1/2B-1/2A
=-5/2A+1/2B
=-5/2(x^2-xy-y^2)+1/2(3xy+x^2)
=-5/2x^2+5/2xy+5/2y^2+3/2xy+1/2x^2
=-5/2x^2+1/2x^2+5/2xy+3/2xy+5/2y^2
=-2x^2+4xy+5/2y^2
=-2*3^2+4*3*(-2)+5/2*(-2)^2
=-18-24+10
=-32
(x-3)^2=0,(y+2)^2=0
x=3
y=-2
1/2[2(A-B)-3A+1/3[3（A+2B）-3A]-1/2A
=1/2[(A-B)-3A+A+2B-3A]-1/2A
=1/2[A-B-3A+A+2B-3A]-1/2A
=1/2[A-3A+A-3A-B+2B]-1/2A
=1/2[-4a+B]-1/2A
=-2A+1/2B-1/2A
=-5/2A+1/2B
=-5/2(x^2-xy-y^2)+1/2(3xy+x^2)
=-5/2x^2+5/2xy+5/2y^2+3/2xy+1/2x^2
=-5/2x^2+1/2x^2+5/2xy+3/2xy+5/2y^2
=-2x^2+4xy+5/2y^2
=-2*3^2+4*3*(-2)+5/2*(-2)^2
=-18-24+10
=-32
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