已知xy的方程组3x 2y=k-1
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![已知xy的方程组3x 2y=k-1](/uploads/image/f/4228226-26-6.jpg?t=%E5%B7%B2%E7%9F%A5xy%E7%9A%84%E6%96%B9%E7%A8%8B%E7%BB%843x+2y%3Dk-1)
x2y+xy2-x-y=xy(x+y)-(x+y)=(x+y)(xy-1)∵x+y=-5,xy=7,∴原式=-5×(7-1)=-30.
解题思路:解关于x,y的方程组,用k表示出x,y,再列不等式求出k解题过程:解:
2x+3y=k①3x-4y=k+11②因为x+y=3∴由①得到:2(x+y)+y=k2×3+y=ky=k-6把y=k-6代入②得:3x-4(k-6)=k+113x-4k+24=k+113x=5k-13
2X=3Y①和3X+4Y=2K+1,②满足方程X+Y=3,③由①,③解得x=9/5,y=6/5,代入②,2k+1=51/5,k=23/5.
因为A+B+C=x3-2y3+3x2y+xy2-3xy+4+y3-x3-4x2y-3xy-3xy2+3+y3+x2y+2xy2+6xy-6=1,所以,对于x、y、z的任何值A+B+C是常数.
①x2y+xy2=xy(x+y)=1×3=3;②x2+y2=(x+y)2-2xy=32-2×1=7.
原式=2x2y+2xy-3x2y-3xy-4x2y=-5x2y-xy当x=-2,y=12时,原式=-9.
∵x+y=6,xy=4,∴x2y+xy2=xy(x+y)=4×6=24.故答案为:24.
x3+y3-x2y-xy2=(x+y)(x2-xy+y2)-xy(x+y)=(x+y)(x2-2xy+y2)=(x+y)(x2+2xy+y2-4xy)=(x+y)[(x+y)2-4xy]=10×(10
那个2是平方吧?可以用^代替原式=x^y+xy^=xy(x+y)=-3*6=-18
由①-②,得x-y-(x+3y)=2k-(3k-1)x-y-x-3y=2k-3k+1-4y=-k+1y=(k-1)/4由①×3+②,得3x-3y+x+3y=6k+3k-14x=9k-1x=(9k-1)
由方程组得x=(2k+3)/7y=(9-2k)/-7又因为x1,所以(2k+3)/71得k的取值范围是2>k>8.
4/33KX=6K,thenX=2;2X+Y=8,thenY=4;2Y=6K,thenK=4/3.
(x+y)(x-y)-y^2+(x-y)^2-(6x^2y-2xy^2)/(2y)=X^2-y^2-y^2+X^2+y^2-2xy-3x^2+xy=-x^2-y^2-xy=-(x^2+y^2+xy-3
x-y=kx+3y=3k-1两个相减4y=2k-1y=k/2-1/4x=3k/2-1/4所以3k/2-1/4>0且k/2-1/4
由题意得(x-2)平方+(y-2)平方+(x-y)平方=0,故x=y=2,故x平方y=8
因为方程组(2K-1)X-(K+1)Y=3K和(4K-1)X-(3K+1)Y=5K+4.所以(4K-1)(2K-1)X-(4K-1)(K+1)Y=3K(4K-1)和(2K-1)(4K-1)X-(2K-
由题意得:3C=A+B=8x2y-6xy2-3xy+7xy2-2xy+5x2y=13x2y+xy2-5xy,∴C=13x2y+xy2−5xy3,故:C-A=13x2y+xy2−5xy3-(8x2y-6
∵x2-y2=xy,∴原式=x2y2+y2x2=x4+y4x2y2=(x2−y2)2+2x2y2x2y2=3x2y2x2y2=3.再问:先化简2a+1/a²-1÷a²-a/a
4x-3y=k①2x+3y=5②①-②×2得:4x-3y-4x-6y=k-10-9y=k-10y=-(k-10)/9①+②得:4x-3y+2x+3y=k+56x=k+5x=(k+5)/6因为x