Acute Angle is an angle that is less than 90 Degrees
Obtuse Angle is an angle that is more than 90 degrees.
The word Acute starts with letter A. And the word Obtuse starts with letter O.
Letter A comes before letter O in alphabets. Similarly Numbers less than 90 come before numbers more than 90. So an Acute angle represents angles less than 90 degrees and an Obtuse Angle represents angles more than 90 degrees.