二元一次方程

(a) 2x-5y=5......1
3x+5y=20.....2
5y=20-3x......3
put3to1
2x-20-3x=5
-x=25
x=-25
so -50-5y=5
-5y=5+50
-y=55/5
y=-11

(a):
2x-5y=5--------(1)
3x+5y=20------(2)

(1)+(2)

5x=25
x=5

Put x=5 into (1)

2(5)-5y=5
10-5=5y
y=1

(b):
0.2x-0.05y=5-------(1)
0.3a+0.05b=20-----(2)

x=0.1a and y=0.01b

0.2(0.1a)-0.05(0.01b)=5
0.02a-0.005b=5
0.2a-0.05b=50------(3)

(2)+(3)

0.5a=70
a=140

Put a=140 into (3)

0.2(140)-0.05b=50
28-0.05b=50
-22=0.05b
b=-440

Hope I can help you!

(a)2x-5y=5 (1)
3x+5y=20 (2)
1+2
5x=25
x=5
Sub (x=5) into (1)
2(5)-5y=5
10-5y=5
y=1

(b)0.2x-0.05y=5 (3)
If x=0.1a & y=0.01b
0.3a+0.05b=20 (4)
By putting x=0.1a & y=0.01b into (3), i.e.
0.2x-0.05y=5 (3)
0.2(0.1a)-0.05(0.01b)=5
0.02a-0.0005b=5
0.2a-0.05b=50 (5)
(4)+(5)
0.5a=75
a=150
Sub (a=150) into (5)
0.2a-0.05b=50
0.2(150)-0.05b=50
0.05b=-20
b=-400