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Use slopes and y-intercepts to determine if the lines 3x−y=4 and −5x+y=4 are parallel.

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Answer: Not parallel

Step-by-step explanation

Solve each equation for y.

  • 3x-y = 4 solves to y = 3x-4
  • -5x+y = 4 solves to y = 5x+4

Compare each result to the slope-intercept form y = mx+b

The slopes are m = 3 and m = 5, which are not equal, which means that the lines are not parallel.

Recall that parallel lines occur when the slopes are equal, but the y intercepts are different. Example: y = 2x+3 and y = 2x+4 are parallel.

Desmos can be used to verify the answer. GeoGebra is another good option. If you prefer using a TI83 or TI84 (or similar), then you can stick to that.

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