The three angles of a triangular ruler are 30, 60, 90 or 45, 45, 90. Yes, that's 30+45=75 (triangle ruler of isosceles right angle+square ruler of 30 degrees and 60 degrees).

Triangle:

A closed figure composed of three line segments that are not on the same straight line is called a triangle. A figure surrounded by three straight lines on a plane or three arcs on a sphere is called a plane triangle; A figure surrounded by three arcs is called a spherical triangle, also known as a triangle.

The closed geometric figure obtained by connecting three line segments end to end is called triangle, which is the basic figure of geometric figure.

Concept:

Triangle is one of the most basic and important figures in plane geometry. A closed figure (including its internal area) consisting of three points on a plane that are not * * lines and line segments connecting each two points. These three points are called the vertices of the triangle; Three line segments are called the sides of a triangle; The angle between every two sides of a triangle and the interior is called the interior angle of the triangle, which is referred to as the angle of the triangle for short; The sum of the three sides is called the perimeter of a triangle.

A triangle is usually represented by its three vertices. For example, a triangle with three vertices A, B and C is recorded as △ABC, which is pronounced as triangle ABC. The three sides and three angles of a triangle are called the basic elements of a triangle.

Angle:

Angle is a mathematical concept. Used to describe the size of an angle, that is, the amount by which either of two intersecting lines must rotate when overlapping with another intersecting line. Degree is a unit to measure the size of an angle, and the symbol is 0.

Basic concepts:

The unit of angle is degree, which is the unit to measure the size of angle, and the symbol is 0. A fillet is divided into 360 equal parts, and each part is defined as 1 degree (1 degree). The number 360 is used for rounded corners because it is easily divisible. 360 has 22 real factors besides 1 and itself, including 2 to 10 except 7, so many special angles are integers.