Example

Classifying {3x2y=4,  y=32x2}\{3x - 2y = 4,\; y = \frac{3}{2}x - 2\} Without Graphing

Determine the number of solutions and classify the system {3x2y=4y=32x2\left\{\begin{array}{l} 3x - 2y = 4 \\ y = \frac{3}{2}x - 2 \end{array}\right. without graphing, by comparing slopes and yy-intercepts.

Second equation: y=32x2y = \frac{3}{2}x - 2 is already in slope-intercept form.

First equation: Convert 3x2y=43x - 2y = 4 to slope-intercept form by isolating yy:

3x2y=43x - 2y = 4

2y=3x+4-2y = -3x + 4

2y2=3x+42\frac{-2y}{-2} = \frac{-3x + 4}{-2}

y=32x2y = \frac{3}{2}x - 2

Compare slopes and y-intercepts:

  • First line: m=32m = \frac{3}{2}, b=2b = -2
  • Second line: m=32m = \frac{3}{2}, b=2b = -2

Because both the slopes and the yy-intercepts are identical, the two equations describe the same line — the lines are coincident.

The system has infinitely many solutions and is consistent and dependent.

This example complements cases where the slopes differ (one solution, consistent and independent) and where the slopes match but the yy-intercepts differ (no solution, inconsistent and independent). Here, matching both slope and yy-intercept confirms that every point on the shared line satisfies both equations.

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Updated 2026-04-21

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