若方程组x 2y=7 k5x-y=k的解
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x2y+xy2-x-y=xy(x+y)-(x+y)=(x+y)(xy-1)∵x+y=-5,xy=7,∴原式=-5×(7-1)=-30.
(x+y)(xy)=x^2y+xy^2=-8原式=-7
3x+2y=2k,①5x+4y=k+3,②②×2-①,得7x+6y=6,③又由题意,得x+y=-5,④联立③④,得方程组7x+6y=6,③x+y=-5,④解得x=36y=-41.代入①,得k=13.
先化简了就很容易解的啊,dx/xy²=dy/x²y即x*dx=y*dy积分得到x²=y²+C2而dx/xy²=dz/zy²即dx/x=dz/
原式=2x2y+2xy-3x2y-3xy-4x2y=-5x2y-xy当x=-2,y=12时,原式=-9.
∵xy+x+y+7=0  
化简得:9-12Y^2+6Y+4+12Y^2+4Y-10-10Y+X-Y+1=X-Y+4带入X、Y值得:=3
根据题意得3x+2y=16k5x-4y=-10k4x-3y=21,消元得x=2ky=5k,代入③得:k=-3.
A+B+C=(x3+3x2y-5xy2+6y3-1)+(y3+2xy2+x2y-2x3+2)+(x3-4x2y+3xy2-7y3+1)=(1+1-2)x3+(3+1-4)x2y+(-5+2+3)xy2
(X+Y)2=1402X2Y*3=14400(X+Y)2=140→X+Y=70→Y=70-X①2X2Y*3=14400→XY=1200②把①代人②得:X(70-X)=1200X²-70X+1
x+2y=7+k①5x-y=k②,把y=-x代入①得x-2x=7+k,解得x=-7-k,把y=-x代入②得5x+x=k,解得x=k6,所以-7-k=k6,解得k=-6.
原式=y(x2+2x+1)=y(x+1)2,故答案为:y(x+1)2.
2x+3y=4k①5x−9y=−k②,①×3+②得:11x=11k,即x=k,将x=k代入①得:y=23k,根据题意得:x+y=k+23k>5,解得:k>3.
∵x+y=5,xy=6,∴x2y+xy2=xy(x+y)=5×6=30.故答案为:30.
x2y+xy2=xy*(x+y)因为x+y=-(7+xy)又x+y=(9+2xy)\3所以(9+2xy)\3=-(7+xy)3+2xy\3=-7-xy5xy\3=-10解得xy=-6所以x+y=-(7
原式=2x2y+2xy-3x2y+3xy-4x2y=-5x2y+5xy,当x=-1,y=1时,原式=-5×(-1)2×1+5×(-1)×1=-5-5=-10.
已知方程组,3x+5y=k①5x+3y=k②,将方程①×5-②×3得,15x+25y-(15x+9y)=5k-3k,解得,y=k8,将y值代入①得,解得,x=k8,∵x+y=2,k8+k8=2,∴k=
∵f(x)=3sin(k5x+π3) ( k≠0)的一条对称轴为x=π6∴f(π6) =±3∴k5×π6+π3=π2+mπ (m∈Z)解得k=30m+5m∈Z
原式=-xy(x-y),当x-y=3,xy=-2时,则原式=-3×(-2)=6.故答案为:6.
如果x,y符号相反,绝对值相等,即y=-x,代入原方程组,得3x-2x=m+1,4x-2x=m-1,即x=m+1,2x=m-1解之,2(m+1)=m-1,得m=-3如果x比y大1,即x=y+1,代入原