中二數學一問(不是求答案)

a + b + c = 4 ...... (1)
2a -b + c=0 ...... (2)
2a + b - 3c = 10 ...... (3)

(1) + (2):
3a + 2c = 4 ...... (4)

(2) + (3):
4a - 2c = 10 ..... (5)

(4) + (5)”
7a = 14
a = 2

把 a = 2 代入 (4):
3(2) + 2c = 4
6 + 2c = 4
2c = -2
c = -1

把 a = 2 及 c = -1 代入 (1):
(2) + b + (-1) = 4
b + 1 = 4
b = 3

答：a = 2, b = 3, c = -1
=

a + b + c = 4 -----(1)
2a -b + c=0 ----- (2)
2a + b - 3c = 10 -----(3)

(1) + (2):
3a + 2c = 4 -----(4)

(2) + (3):
4a - 2c = 10 -----(5)

(4) + (5)
7a = 14
a = 2

Sub.a = 2 into(4):
3(2) + 2c = 4
6 + 2c = 4
2c = -2
c = -1

Sub. a = 2 and c = -1 into (1):
2 + b + (-1) = 4
b + 1 = 4
b = 3

the solution is a = 2, b = 3 and c = -1