解二元一次方程组1.{5x-3y=16 ① {x-y=3 ①2.{2x-5y=-21 ①{4x+3y=23②3.{4x+

.{5x-3y=16 ①
{x-y=3 ②
①-②×3,得
2x=7；x=3.5
3.5-y=3；y=0.5
{2x-5y=-21 ①
{4x+3y=23 ②
②-①×2,得
13y=65；y=5
2x-25=-21；x=2
{4x+7y=-19 ①
{4x-5y=17②
①-②,得
12y=-36；y=-3
4x+（-21）=-19；x=0.5
4、x+y+z=26 ① x-y=1 ② 2x-y+z=18 ③
③-①,得
x-2y=-8；(x-y)-y=-8；1-y=-8；y=9
将y=9代入②,得
x-9=1；x=10
10+9+z=26；z=7