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Verifying that y=2x+3y = -2x + 3 and 2x+y=12x + y = -1 are Parallel

To determine whether the lines y=2x+3y = -2x + 3 and 2x+y=12x + y = -1 are parallel, convert both equations to slope-intercept form and compare their slopes and yy-intercepts.

First equation: y=2x+3y = -2x + 3 is already in slope-intercept form. The slope is m=2m = -2 and the yy-intercept is (0,3)(0, 3).

Second equation: Solve 2x+y=12x + y = -1 for yy by subtracting 2x2x from both sides:

y=2x1y = -2x - 1

The slope is m=2m = -2 and the yy-intercept is (0,1)(0, -1).

Compare slopes and yy-intercepts:

  • First line: m=2m = -2, b=3b = 3
  • Second line: m=2m = -2, b=1b = -1

Because both lines have the same slope (2-2) but different yy-intercepts (33 vs. 1-1), the lines are parallel. When both lines are graphed on the same coordinate plane, they appear as two distinct lines that never cross. This demonstrates that by writing both equations in slope-intercept form, parallelism can be confirmed by inspection — without needing to graph the lines — simply by checking that the slopes match and the yy-intercepts differ.

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Updated 2026-04-21

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