notice the angle at R and T, they're less than 90°.
now the angle at S is more than 90°, the angle at S is not a right-angle, and is not an acute angle either, is an obtuse angle. That makes the triangle likewise.
A triangle with three acute angles is an acute triangle. A triangle with two acute angles and one right angle is a right triangle. A triangle with two acute angles and an obtuse angle is an obtuse triangle.
This triangle has an obtuse angle, so it is an obtuse triangle. That is how it is classified according to angles.
According to side lengths, this triangle has sides of three different lengths, so it is a scalene triangle.
