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
来源:学生作业帮助网 编辑:作业帮 时间:2024/06/30 08:49:10
![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](/uploads/image/z/2097298-10-8.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%E5%86%8D%E6%B1%82%E5%80%BC%EF%BC%9A%E8%AE%BE%EF%BC%9AA%3D2x%5E2-3xy%2By%5E2-x%2B2y+B%3D4x%5E2-6xy%2B2y%5E2-3x-y+%2C%E8%8B%A5%2Fx-3a%2F%2B%28y%2B5%29%5E2%3D0%2C%E4%B8%94B-2A%3Da%3B%E6%B1%82A%E7%9A%84)
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
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
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
∵|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
由/x-3a/+(y+5)^2=0 得
x=2a,y=-5
将x、y值代入A、B
A=8a^2+30a+25-2a-10=8a^2+28a+15
B=16a^2+60a+50-6a+5=16a^2+54a+55
根据B-2A=a
16a^2+54a+55-(16a^2+56a+30)=a
-2a+25=a
-3a=-25
a=25/3
将a=25/3代入A即可求出A的值
A 的什么,说清楚啊
求A的值?