How to Determine If Two Lines Are Parallel or Perpendicular

It is often the case that when you construct lines, two lines may look parallel or perpendicular, when in fact they aren’t. GeoMaster on the TI-84 Plus graphing calculator can determine whether lines are parallel or perpendicular for you.

To get GeoMaster to determine if two lines are perpendicular or parallel, follow these steps:

  1. Select the Perpendicular? or Parallel? tool from the MISC menu.

    To do this, press [GRAPH][GRAPH], use the arrow keys to move the cursor to the appropriate tool, and press [ENTER]. The tool you selected appears in the upper-right corner of the screen where the Perpendicular? tool or Parallel? tool shows as active.

  2. Use the arrow keys to move the cursor to the first line and press [ENTER]. Move the cursor to the second line and press [ENTER]. The conclusion as to whether or not the lines are parallel or perpendicular appears on the screen.

    The two selected lines appear as dashed lines. The word “true” appearing on the screen in this picture indicates that the lines are indeed perpendicular.

  3. If you want to use the same tool to test another pair of lines, press [CLEAR] and then repeat Step 2.

    The word “false” appearing on the screen indicates that the lines are not perpendicular.

  4. When you are finished using the Perpendicular? or Parallel? tool, deactivate it by pressing [CLEAR] two times or by selecting another menu item.

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