You should remember that the value of an acute angle needs to be found in interval `(0^o,90^o)` expressed in degrees or `(0^o,pi/2)` expressed in radians.
Notice that the interval does not include the value of `90^o` , since an angle that measures `90^o` is no more an acute angle, but a right angle.
If the angle is larger than 90^o but smaller than `180^o` , then, the angle is obtuse. Notice that the angle that measures exactly `180^o` is a straight angle.
You also should remember that you may identify different types of triangles, based on angles classification such that:
- acute triangle with all three angles less than `90^o`
- right triangle with an angle of `90^o`
- obtuse triangle with an angle larger than `90^o` but smaller than `180^o` .
An angle that measures anything between 0 degrees and 90 degrees is called an acute angle.
So angles that measure less than 90 degrees, (for example they could be 89.9degrees, 15 degrees, 0.15 degrees, 30 degrees) are all acute angles.
If you find that an angle measures 90degrees, it's a Right angle.
Those measuring more than 90degrees are called obtuse angles.
If an angle measures 180 degrees , it is called a straight angle.
Those measuring between 180 and 360 degrees are called reflex angles.