Example

Solving {5x2y=10,  y=52x}\{5x - 2y = -10,\; y = \frac{5}{2}x\} by Substitution

Solve the system {5x2y=10y=52x\left\{\begin{array}{l} 5x - 2y = -10 \\ y = \frac{5}{2}x \end{array}\right. using the substitution method.

The second equation is already solved for yy, so Step 1 is already complete.

Step 2 — Substitute into the other equation. Replace yy in the first equation with 52x\frac{5}{2}x:

5x2(52x)=105x - 2\left(\frac{5}{2}x\right) = -10

Step 3 — Solve the resulting one-variable equation. Simplify 252x=5x-2 \cdot \frac{5}{2}x = -5x:

5x5x=105x - 5x = -10

0=100 = -10

Because 0=100 = -10 is a false statement — and the variable has been completely eliminated — the equations are inconsistent. The two lines are parallel and never intersect, so the system has no solution.

This example illustrates the algebraic indicator of an inconsistent system: when the substitution process eliminates all variables and produces a false numerical statement such as 0=100 = -10, no ordered pair can satisfy both equations simultaneously. This contrasts with the dependent case, where the same elimination produces a true statement like 0=00 = 0.

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Updated 2026-04-21

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