Consistency Examples in Math

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Consistency.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Math.

Concept Recap

A system of equations is consistent when there exists at least one set of variable values that satisfies every equation simultaneously.

The constraints don't contradict each otherβ€”there's some answer that works.

Read the full concept explanation β†’

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Consistent means 'solvable'; inconsistent means 'no solution exists.'

Common stuck point: Inconsistency often shows as 0 = 5 or similar contradiction.

Sense of Study hint: Simplify the system fully. If you reach a statement like 0 = 5, stop and declare no solution exists.

Worked Examples

Example 1

easy
Is the system \begin{cases} x + y = 5 \\ 2x + 2y = 8 \end{cases} consistent?

Solution

  1. 1
    Step 1: Simplify equation 2: x + y = 4.
  2. 2
    Step 2: Compare: x + y = 5 and x + y = 4. Contradiction!
  3. 3
    Step 3: No values of x, y satisfy both. The system is inconsistent.

Answer

Inconsistent (no solution)
A system is consistent if at least one solution exists. Here the two equations demand x + y equal both 5 and 4 simultaneously, which is impossible.

Example 2

medium
For what value of k is \begin{cases} x + 2y = 3 \\ 2x + 4y = k \end{cases} consistent?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Is \begin{cases} 3x - y = 7 \\ x + 2y = 1 \end{cases} consistent?

Example 2

medium
Is \begin{cases} x + y + z = 1 \\ x + y + z = 3 \end{cases} consistent?

Background Knowledge

These ideas may be useful before you work through the harder examples.

systems of equations