聽日要交既聯立二元一次方程急!!20分

1. 唔知你有冇打錯題目
3x+2y = 0 ---(1)
5x+y = 13
y = 13-5x ---(2)
將 (2) 代入 (1):
3x+2(13-5x) = 0
3x+26-10x = 0
7x = 26
x = 26/7
將 x = 26/7 代入 (2):
y = 13-5(26/7) = -39/7
2. 4x-3y = 17 ---(1)
2x-5y = 19 ---(2)
(2)*2: 4x-10y = 38 ---(3)
(1)-(3): -3y-(-10y) = 17-38
7y = -21
y = -3
將 y = -3 代入 (1):
4x-3(-3) = 17
4x = 8
x = 2
3. 2a+3b = 33 ---(1)
3a-4b = 24 ---(2)
(1)*3: 6a+9b = 99 ---(3)
(2)*2: 6a-8b = 48 ---(4)
(3)-(4): 9b-(-8b) = 99-48
17b = 51
b = 3
將 b = 3 代入 (1):
2a+3(3) = 33
2a = 24
a = 12
4. 2a+3b = 2 ---(1)
5a-4b = 5 ---(2)
(1)*5: 10a+15b = 10 ---(3)
(2)*2: 10a-8b = 10 ---(4)
(3)-(4): 15b-(-8b) = 10-10
23b = 0
b = 0
將 b = 0 代入 (1):
2a+3(0) = 2
2a = 2
a = 1

1.3x+2y=0
2y=-3x
y=-3x/2

代y= -3x/2