Drawing a reflex angle involves drawing the smaller, associated angle first and then indicating the larger angle that completes the full circle. The most common method relies on the fact that a full circle is 360 degrees.
Understanding Reflex Angles
A reflex angle is an angle that measures more than 180 degrees but less than 360 degrees. Because standard protractors usually only measure angles up to 180 degrees, you draw a reflex angle by drawing the part that is not the reflex angle – the angle that adds up to 360 degrees with the reflex angle.
The Method for Drawing a Reflex Angle
The core idea is to subtract the desired reflex angle from 360 degrees to find the size of the angle you can draw with a standard protractor.
Step-by-Step Guide
Here is the process to draw a reflex angle:
- Calculate the Complementary Angle: Subtract the given reflex angle from 360°. This gives you the size of the angle that, when added to the reflex angle, makes a full circle. This smaller angle is typically less than 180°.
- Draw the Calculated Angle: Using a ruler and protractor, draw the angle you calculated in Step 1. Start by drawing a straight line segment (the initial arm of the angle). Place the protractor's center on one endpoint of the line (the vertex) and align the base with the line. Mark the point corresponding to the calculated angle measurement and draw a second line segment from the vertex through this point (the terminal arm).
- Indicate the Reflex Angle: The reflex angle is the larger angle around the vertex, on the outside of the angle you just drew. You indicate this reflex angle by drawing a large arc starting from the initial arm and sweeping clockwise or counter-clockwise around the outside, ending at the terminal arm.
Example: Drawing a 240° Reflex Angle
Let's walk through an example, as referenced:
- Step 1: Subtract the given reflex angle from 360°. In this case, it gives us 360° - 240° = 120°. This means the angle you will draw with the protractor is 120°.
- Step 2: Draw and mark this angle using the protractor. Draw a 120° angle using your protractor.
- Step 3: Indicate the Reflex Angle. The 240° reflex angle is the angle on the outside of the 120° angle you drew. Draw an arc on the outside to show that you are referring to the 240° angle.
This method allows you to accurately represent a reflex angle using standard drawing tools.
