You need to use an protractor which is an object you use to measure angles and just for some basic info. An acute angle is an angle that is less than 90 degrees. A right angle should be exactly 90 degrees. An obtuse angle is over 90 degrees but isn't over 180 degrees. A straight angle is 180 degrees. A reflex angle is 180 degrees to 360 degrees. 360 degrees is a perfect circle.