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Example

Verifying that y=4y = -4 and y=3y = 3 are Parallel

To determine whether the horizontal lines y=4y = -4 and y=3y = 3 are parallel, rewrite each equation in slope-intercept form and compare slopes and yy-intercepts.

First equation: Since there is no xx term, write y=4y = -4 as y=0x4y = 0x - 4 to make the slope explicit. The slope is m=0m = 0 and the yy-intercept is (0,4)(0, -4).

Second equation: Similarly, write y=3y = 3 as y=0x+3y = 0x + 3. The slope is m=0m = 0 and the yy-intercept is (0,3)(0, 3).

Compare slopes and yy-intercepts:

  • First line: m=0m = 0, yy-intercept (0,4)(0, -4)
  • Second line: m=0m = 0, yy-intercept (0,3)(0, 3)

Because both lines have the same slope (00) but different yy-intercepts (4-4 vs. 33), the lines are parallel.

Alternatively, recognizing immediately that both equations have the form y=by = b reveals that both are horizontal lines. All horizontal lines have slope 00, and since they cross the yy-axis at different heights (4-4 and 33), they never intersect and are therefore parallel.

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Updated 2026-04-21

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