According to the classification of angles, an angle equal to 90 is a right angle, an angle greater than 0 and less than 90 is an acute angle, and an angle greater than 90 and less than180 is an obtuse angle.
Because every horizontal and vertical line in the grid is vertical, that is, the included angle is a right angle, according to this feature, it is easy to draw a right angle, and then draw a ray inside the right angle at the vertex of the right angle to get an acute angle, and draw a ray outside the right angle to get an obtuse angle.
Extended data:
When the angle changes from 90 to180, the sine value decreases (or increases) with the increase (or decrease) of the angle, and the cosine value decreases (or increases) with the increase (or decrease) of the angle. Tangent value increases (or decreases) with the increase (or decrease) of angle, and cotangent value decreases (or increases) with the increase (or decrease) of angle; Secant value increases (or decreases) with the increase (or decrease) of angle, and cotangent value increases (or decreases) with the increase (or decrease) of angle.
Baidu encyclopedia-obtuse angle