中2數 聯立二元一次方程 教教我吧...

1. {x+y = 43
{x-y = 5

2x=48
x=24,y=19

2.y=89/2
x= 11 + 89/2
= 111/2

3.{x-y = 5
{3(x+y)=21 ->x+y =7
2x =12
x=6 , y=1

4.蘋果=x 梨=y
{2x+3y = 335
{x+y=150 -> 2x+2y = 300
y=35
x=115

5. x=0
y=13

6.長=x  闊=y
{x=2y+1
{2x+2y = 26
3x = 27
x = 9
y=4

7.見Q4

8. {1.3x+1.3y=52
{1.3x+2.1y=64
0.8y = 12
y = 15
x= 25