It just means at right angles (90°) to.
The red line is perpendicular to the blue line:
(The little box drawn in the corner, means “at right angles”, so we didn’t really need to also show that it was 90°, but we just wanted to!)
Try for yourself:
Lines are parallel if they are always the same distance apart (called “equidistant”), and will never meet. (They also point in the same direction). Just remember:
Always the same distance apart and never touching.
The red line and blue line are parallel in both these examples:
Try it yourself:
Perpendicular to Parallel
Question: What is the difference between perpendicular and parallel?
Answer: 90 degrees (a right angle)
That’s right, when we rotate a perpendicular line by 90° it becomes parallel (but not if it touches!)
Rotate One Line 90°
… Parallel !
Likewise, parallel lines become perpendicular when one line is rotated 90°.
Curves can also be parallel when they keep the same distance apart (called “equidistant”), like railroad tracks.
The red curve is parallel to the blue curve in both these cases:
Surfaces can also be parallel, like this:
Lines and Planes
Advanced Topic: You can also learn about Parallel and Perpendicular Lines and Planes
An Interior Angle is an angle inside a shape
Note: When we add up the Interior Angle and Exterior Angle we get a straight line, 180°. (See Supplementary Angles
The Exterior Angle is the angle between any side of a shape, and a line extended from the next side.
When we add up the Interior Angle and Exterior Angle we get a straight line 180°. They are “Supplementary Angles”.