Balanced Trade 1D7A76
1. **Problem statement:** We have a trade matrix $$A = \begin{pmatrix} 0.15 & 0.5 & 0.25 \\ 0.35 & 0.3 & 0.45 \\ 0.5 & 0.2 & 0.3 \end{pmatrix}$$ and budgets vector $$\vec{x} = \begin{pmatrix} x_1 \\ x_2 \\ x_3 \end{pmatrix}$$ with the condition $$A\vec{x} = \vec{x}$$ representing balanced deficit-free trade. Given $$x_1 = 2000$$, find $$x_2$$ and $$x_3$$.
2. **Formula and explanation:** The equation $$A\vec{x} = \vec{x}$$ means $$\vec{x}$$ is an eigenvector of $$A$$ corresponding to eigenvalue 1. Writing out the system:
$$
\begin{cases}
0.15 x_1 + 0.5 x_2 + 0.25 x_3 = x_1 \\
0.35 x_1 + 0.3 x_2 + 0.45 x_3 = x_2 \\
0.5 x_1 + 0.2 x_2 + 0.3 x_3 = x_3
\end{cases}
$$
Rearranged:
$$
\begin{cases}
0.15 x_1 + 0.5 x_2 + 0.25 x_3 - x_1 = 0 \\
0.35 x_1 + 0.3 x_2 + 0.45 x_3 - x_2 = 0 \\
0.5 x_1 + 0.2 x_2 + 0.3 x_3 - x_3 = 0
\end{cases}
$$
Simplify each:
$$
\begin{cases}
-0.85 x_1 + 0.5 x_2 + 0.25 x_3 = 0 \\
0.35 x_1 - 0.7 x_2 + 0.45 x_3 = 0 \\
0.5 x_1 + 0.2 x_2 - 0.7 x_3 = 0
\end{cases}
$$
3. **Substitute known value:** $$x_1 = 2000$$, so:
$$
\begin{cases}
-0.85 \times 2000 + 0.5 x_2 + 0.25 x_3 = 0 \\
0.35 \times 2000 - 0.7 x_2 + 0.45 x_3 = 0 \\
0.5 \times 2000 + 0.2 x_2 - 0.7 x_3 = 0
\end{cases}
$$
Calculate constants:
$$
\begin{cases}
-1700 + 0.5 x_2 + 0.25 x_3 = 0 \\
700 - 0.7 x_2 + 0.45 x_3 = 0 \\
1000 + 0.2 x_2 - 0.7 x_3 = 0
\end{cases}
$$
4. **Rewrite system:**
$$
\begin{cases}
0.5 x_2 + 0.25 x_3 = 1700 \\
-0.7 x_2 + 0.45 x_3 = -700 \\
0.2 x_2 - 0.7 x_3 = -1000
\end{cases}
$$
5. **Solve first two equations for $$x_2$$ and $$x_3$$:**
From first:
$$0.5 x_2 = 1700 - 0.25 x_3 \Rightarrow x_2 = \frac{1700 - 0.25 x_3}{0.5} = 3400 - 0.5 x_3$$
Substitute into second:
$$-0.7 (3400 - 0.5 x_3) + 0.45 x_3 = -700$$
$$-2380 + 0.35 x_3 + 0.45 x_3 = -700$$
$$-2380 + 0.8 x_3 = -700$$
$$0.8 x_3 = 1680$$
$$x_3 = \frac{1680}{0.8} = 2100$$
6. **Find $$x_2$$:**
$$x_2 = 3400 - 0.5 \times 2100 = 3400 - 1050 = 2350$$
7. **Check with third equation:**
$$0.2 \times 2350 - 0.7 \times 2100 = 470 - 1470 = -1000$$ which matches the right side.
**Final answer:** $$x_2 = 2350$$ and $$x_3 = 2100$$.