{2x+3y=15.5 5x+6y=35

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{2x+3y=15.55x+6y=35{2x+3y=15.55x+6y=35{2x+3y=15.55x+6y=352x+3y=15.5……（1）5x+6y=35…………（2）（1）×2－（2）得x=4

{2x+3y=15.5 5x+6y=35
{2x+3y=15.5 5x+6y=35

{2x+3y=15.5 5x+6y=35
2x+3y=15.5 ……（1）
5x+6y=35…………（2）
（1）×2－（2）得
x=4
由（1）式得
y=(15.5-2x)/3=(15.5-8)/3=2.5

方程1*2得:4x+6y=31再减去方程2得-x=-4,x=4,代入方程1得y=1.5所以x=4,y=1.5

x=4,y=2.5

解:由1式乘以2得:4X+6Y=30
再由2式减去1式得 X=4
把X=4代入1式得 Y=2.5

x+y/2+x-y/6=5 2(x+y)-3(x-y)=-2 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 例X=1 y=21.X+Y=5 X-Y=15 2.2X+3Y=4 5X+6Y=7 3.X+3Y=5 3X+Y=-1 4.2X+Y=3 3X+5Y=11 5.4X+3Y=6 2X+Y=4 6.X+Y=180 X=3Y-10 7.3X-2Y=3 2X-Y=7 8.5X+3Y=7Y X+Y=45 9.3X+4Y=126X+8Y=24 X:6Y=1:4 10.X+Y=138 X-45=Y+53 11.X+Y=60 14Y=20X 12.2X+3Y=15.5 5X+6Y=35 13.X+Y=170 3 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= 3x+5y-(x+y)=6 2(x+y)-3x=-7 把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)= 3(x-y)把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)=3(x-y)²-4(x-y)+7(x-y)-6(x-y)²= x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 （x+y）/2- x-y/2=6 3(x+y)=4(x-y) x+y/3+x-y/2=6 4(x+y)-2(x-y)=40 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 2(x+y)-3(x-y)=1 6(x+y)+(x-y)=51 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27