明天要交聯立二元方程功課!20分!!

5.{2x+y=14 --> (1)
{5x+3y=38 --> (2)
From (1)
x = (14-y) / 2--> (3)
Sub. (3) into (2)
5 [(14-y) / 2] +3y = 38
y = 6
Sub. y=12 into (3)
x = (14-6) / 2
x = 4

6.{2a+5b=11 --> (1)
{4a+3b=1 --> (2)
From (1)
a = (11-5b) / 2 --> (3)
Sub. (3) into (2)
4 [(11-5b) / 2] +3b = 1
b = 3
Sub. b=3 into (3)
a = (11-5x3) / 2
a = -2

7.{x+3y=7 --> (1)
{3x-2y+12=0 --> (2)
From (1)
x = 7-3y --> (3)
Sub. (3) into (2)
3(7-3y)-2y+12 = 0
y = 3
Sub. y=3 into (3)
x = 7 - 3x3
x = -2