Question

2(x十y)一3(x一y)=3，4(x十y)十3x=15十3y

Answer 1

2(x+y)-3(x-y) = 3 (1)
4(x+y)+3x = 15 + 3y (2)
整理原方程组得：
2(x+y)-3(x-y) = 3 (3)
4(x+y)+3(x-y) = 15 (4)
(3)+(4)得，　　6(x+y) = 18 解得：　x + y = 3 (5)
把　x + y = 3代入（3）得 x - y = [2(x+y)-3]/3 = （2×3 －3）/3 = 1
即 x - y = 1 (6)
(5) + (6)得， 2x = 4 解得 x = 2
把 x = 2代入（5）得 y = 1
所以，原方程组的解是：x =2 y = 1