Question

How to identify acute and obtuse triangle by side lengths?

Answer 1

Acute angle is smaller than 90 degrees while obtuse angle is more than 90 degrees but smaller than 180 degrees 

For example 45 and 60 are acute angles 

while 120 and 150 are obtuse angles 

Answer 2

by the protector ( d) it helps you cheak it is acute or obtuse
acute = angle smaller than 90°
obtuse = angle smaller than 180°
reflex = angle smaller than 360°