5x2*3xy=
已知x2-xy=3,xy-y2=-5,试求代数式x2+2xy-3y2的值.
如果M=3x2-2xy-4y2,N=4x2+5xy-y2,则8x2-13xy-15y2等于( )
已知x2+y2=7,xy=-2,求5x2—3xy—4y2—11xy—7x2+2y2的值
已知x2+y2 =7,xy=-2.求5x2 -3xy-4y2 -11xy-7x2 +2y2
已知X2+y2=7,Xy=-2,求多项式5X2一3Xy-4y2-11Xy-7X2+2y2的值.
已知:x2+y2=7,xy=-2.求7x2-3xy-2y2-11xy-5x2+4y2的值.
先化简,再求值:(1)2x2-5x x2 4x,其中x=-3 (2)(3x2-xy-2y2)-2(x2 xy-2y2),
(8xy-3x2)-5xy-3(xy-2x2+3)
计算:12xy+(3x2-5xy)-2(3xy+2x2).
已知:x2+y2=7,xy=-2.求7x2-3xy-2y2-11xy-5x2+4y2已知:x2+y2=7,xy=-2.求
已知,A=3x2+3y2-5xy,B=2xy-3y2+4x2,求:
已知:x=3,y=-5,x2-2xy+y2/x2-y2的值是