已知x2-xy=-3,2xy-y2=-8,求2x2+4xy-3y2 的值.
来源:学生作业帮助网 编辑:作业帮 时间:2024/09/21 22:17:30
x2-xy=-3①,2xy-y2=-8②,①×2+②×3得:2x2-2xy+6xy-3y2=-6-24=-30,则2x2+4xy-3y2=-30.
∵2(x2+xy)-3(xy+y2)=2x2-xy-3y2,∴2x2-xy-3y2=2×3-3×(-2)=12.故选A.
x2+y2+3xy=(x+y)2+xy,∵x+y=4,xy=2,∴x2+y2+3xy=42+2=18.故答案为18.
∵x2+xy=-3,xy+y2=7,∴(x2+xy)+(xy+y2)=-3+7=4,即x2+2xy+y2=4.
5x2—3xy—4y2—11xy—7x2+2y2=-2x2-2y2-14xy=-2(x2+y2)-14xy=-14+28=14
x+y=7xy=27^2=(x+y)^2=x^2+2xy+y^2=x^2+y^2+2*2x^2+y^2=45(1)y=7-xx(7-x)=2x^2-7x+2=0x=(7+41^(1/2))/2或x=(
再问:你确定吗?再答:我保证再答:亲,那一步不明白可以问再问:你省略了一步吧!再答:能看明白吗再问:no再答: 再答:是不是这部再问:那么第一步是怎么得来的呢?再答:第一步不是你
(1)A-2B=2x2+3xy+2y-1-2(x2−xy+x−12)=2x2+3xy+2y-1-2x2+2xy-2x+1=5xy+2y-2x,当x=y=-2时,A-2B=5xy+2y-2x=5×(-2
∵x+y=4,xy=2,∴x2+y2+3xy,=(x+y)2+xy,=42+2,=18.
有x2+xy=3可得,2x2+2xy=6 (1),有xy+y2=-2得,3xy+3y2=-6 (2),根据分析,(1)-(2)可得,2x2-xy-3y2=6-(-6)=
x2+2xy-3y2=x2-xy+3xy-3y2=x2-xy+3(xy-y2),∵x2-xy=3,xy-y2=-5,∴x2+2xy-3y2=3+3×(-5)=-12.
根据题意,2x2-3xy+y2=0,且xy≠0,故有(yx)2−3yx+2=0,即(yx−1)(yx−2)=0,即得yx=1或2,故xy=1或12,所以xy+yx=2或212.故选A.
7x2-3xy-2y2-11xy-5x2+4y2=2x²-14xy+2y²=2(x²+y²)-14xy=2×7-14×(-2)=14+28=42
∵2x2+xy-3y2=0(y≠0),即(2x+3y)(x-y)=0,∴2x+3y=0,x-y=0,解得:x=-32y,x=y,当x=-32y时,xy=-32;当x=y时,xy=1.
∵x2+y2=7,xy=-2,∴7x2-3xy-2y2-11xy-5x2+4y2,=(7x2-5x2)+(4y2-2y2)-(3xy+11xy),=2x2+2y2-14xy,=2(x2+y2)-14x
6x2-xy-15y2=(2x+3y)(3x-5y)=0,所以x=-3/2y或x=5/3y
由xy=27得,x=27y,∴x2−3xy+2y22x2−3xy+7y2=449y2−67y2+2y2849y2−67y2+7y2=60309=20103.故选C.
2x²-xy-3y²=2x²+2xy-3xy-3y²=2(x²+xy)-3(xy+y²)已知x²+xy=3,xy+y²=
0.X^2+XY=3;(1)XY+Y^2=2;(2)2*(1)-3*(2)=2*X^2-XY-3*Y^2=2*3-3*2=0