X+Y=5,2X+Y=8 .4X+3Y=5,X-2Y=4 .这2题用带如消元法解

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/05/15 05:57:17

X+Y=5,2X+Y=8 .4X+3Y=5,X-2Y=4 .这2题用带如消元法解
7X-2Y=3,9X+2Y=-19 用加减消元法解

1.代入消元法
x+y=5,y=5-x代入2x+y=8
2x+（5-x）=8解出x=3,y=5-x=2
x=3,y=2
由x-2y=4得x=4+2y代入4x+3y=5
4（4+2y）+3y=5,y=-1
y=-1代入x=4+2y=4-2=2
x=2,y=-1
2.加减消元：
两个式子相加,就削去了y
7x+9x=3-19
16x=-16
x=-1
代入其中任何一个可以算出y,y=-5
x=-1,y=-5

3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuai 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( 数学题……555{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y 已知x*x+4x+y*y-2y+5=0,则x*x+y*y=? 先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y 方程组x-2y=8,3x-4y=5,x=?,y=? 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y* 已知x²+y²+5=2x+4y,求【2x²-(x-y)(x-y)】【(x+y-1)(x-y {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1