Chapter 10.2 - Lines in Space

Perpendicular Lines

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If two lines are perpendicular, the true angle between them is 90 degrees. In orthographic views, two lines are perpendicular if, in a view where either of the lines appears TL, the angle between the lines is 90 degrees. In case #1, the lines are not perpendicular, even though a 90 degree angles appears in the top view. In case #2, the lines are perpendicular.