This one’s a right angled triangle, where one angle is always a right angle, so that's 90 degrees. All triangles have internal angles that add up to 180°, no matter the type of triangle.

Speed squares are a helpful saw guide for cutting 45- and 90-degree angles. The plastic squares ... It features ¼-inch ...

For example, an acute triangle will have three angles less than 90 degrees, where as an obtuse triangle will have one angle greater than 90 degrees.