We are given a system of equations involving absolute values: $|x| + |y-1| = 1$ $x + 2y = 3$

AlgebraAbsolute Value EquationsSystems of EquationsCase Analysis
2025/5/26

1. Problem Description

We are given a system of equations involving absolute values:
x+y1=1|x| + |y-1| = 1
x+2y=3x + 2y = 3

2. Solution Steps

First, we can express xx in terms of yy from the second equation:
x=32yx = 3 - 2y
Now we consider different cases for the absolute values:
Case 1: x0x \ge 0 and y10y-1 \ge 0 (i.e., y1y \ge 1)
In this case, x=x|x| = x and y1=y1|y-1| = y-1. Thus, the first equation becomes:
x+y1=1x + y - 1 = 1
x+y=2x + y = 2
Substituting x=32yx = 3 - 2y, we have:
(32y)+y=2(3 - 2y) + y = 2
3y=23 - y = 2
y=1y = 1
Then, x=32(1)=32=1x = 3 - 2(1) = 3 - 2 = 1.
Since x=10x = 1 \ge 0 and y=11y = 1 \ge 1, this is a valid solution. So (x,y)=(1,1)(x, y) = (1, 1) is a solution.
Case 2: x<0x < 0 and y10y-1 \ge 0 (i.e., y1y \ge 1)
In this case, x=x|x| = -x and y1=y1|y-1| = y-1. Thus, the first equation becomes:
x+y1=1-x + y - 1 = 1
x+y=2-x + y = 2
Substituting x=32yx = 3 - 2y, we have:
(32y)+y=2-(3 - 2y) + y = 2
3+2y+y=2-3 + 2y + y = 2
3y=53y = 5
y=53y = \frac{5}{3}
Then, x=32(53)=3103=9103=13x = 3 - 2(\frac{5}{3}) = 3 - \frac{10}{3} = \frac{9 - 10}{3} = -\frac{1}{3}.
Since x=13<0x = -\frac{1}{3} < 0 and y=531y = \frac{5}{3} \ge 1, this is a valid solution. So (x,y)=(13,53)(x, y) = (-\frac{1}{3}, \frac{5}{3}) is a solution.
Case 3: x0x \ge 0 and y1<0y-1 < 0 (i.e., y<1y < 1)
In this case, x=x|x| = x and y1=(y1)=1y|y-1| = -(y-1) = 1-y. Thus, the first equation becomes:
x+1y=1x + 1 - y = 1
xy=0x - y = 0
x=yx = y
Substituting x=32yx = 3 - 2y, we have:
32y=y3 - 2y = y
3=3y3 = 3y
y=1y = 1
Then, x=1x = 1.
However, we assumed y<1y < 1, so y=1y = 1 contradicts this assumption. Thus, there is no solution in this case.
Case 4: x<0x < 0 and y1<0y-1 < 0 (i.e., y<1y < 1)
In this case, x=x|x| = -x and y1=(y1)=1y|y-1| = -(y-1) = 1-y. Thus, the first equation becomes:
x+1y=1-x + 1 - y = 1
xy=0-x - y = 0
x=yx = -y
Substituting x=32yx = 3 - 2y, we have:
32y=y3 - 2y = -y
3=y3 = y
Then, x=3x = -3.
However, we assumed y<1y < 1, so y=3y = 3 contradicts this assumption. Thus, there is no solution in this case.
Therefore, the solutions are (1,1)(1, 1) and (13,53)(-\frac{1}{3}, \frac{5}{3}).

3. Final Answer

The solutions are (1,1)(1, 1) and (13,53)(-\frac{1}{3}, \frac{5}{3}).

Related problems in "Algebra"