The four types of angle you should know are acute, obtuse, reflex and right angles. When you are estimating an angle, you should consider what type of angle it is first.

ANGALS

Acute Anglean angle that is less than 90°Right Anglean angle that is 90° exactlyObtuse Anglean angle that is greater than 90° but less than 180°Straight Anglean angle that is 180° exactlyReflex Anglean angle that is greater than 180°

this is an acute angle

this is a right angal.

180 degrees.