How do you know which set of numbers on a protractor you are suppose to use when measuring angles on a circle graph?

Answer 1

Assuming you've got a 180o protractor (and not a 360o angle measurer).

To measure an acute, right or obtuse angle (ie 0o to 180o):

1. Place the centre mark of the protractor on the centre of the angle (ie where the arms of the angle meet)
2. Put one of the base lines (which will be marked 0o and 180o) on one of the arms of the angle, so that the other line of the angle is within the scale of the protractor.
3. Use the scale which starts with 0o on the first arm to read off the angle to the other arm.

To measure a reflex angle (ie 180o to 360o):

1. Place the protractor centre as above
2. Put the base line as above
3. Use the scale which starts with 180o on the first arm to read off the angle to the other arm.
4. Add 180o to the angle found in step 3.