The first triangle has three acute angles; The second triangle has a right angle and two acute angles; The third triangle has two acute angles and an obtuse angle. Each triangle has at least two acute angles. The third angle can be an acute angle, a right angle or an obtuse angle.

1. triangle

Triangle is a closed figure composed of three line segments on the same plane but not on the same straight line, which has applications in mathematics and architecture.

Ordinary triangles are divided into ordinary triangles (three sides are unequal) and isosceles triangles (isosceles triangles with unequal waist and bottom and isosceles triangles with equal waist and bottom, that is, equilateral triangles); According to the angle, there are right triangle, acute triangle and obtuse triangle, among which acute triangle and obtuse triangle are collectively called oblique 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. A closed geometry consisting of three line segments connected end to end is called a triangle. Triangle is the basic figure of geometric figure.

2. acute angle

An acute angle refers to an angle (right angle) greater than 0 and less than 90, and an acute angle is a bad angle. The sum of the two acute angles is not necessarily greater than the right angle, but it must be less than the right angle. The acute angle must be the first quadrant angle, and the first quadrant angle is not necessarily the acute angle.

A triangle with three acute angles is called an acute triangle. In an acute triangle, every internal angle is acute, and the sum of any two internal angles is greater than the right angle; Each side is sandwiched between its adjacent side and the product sum quotient of cosine of their included angle, and the sum of squares of any two sides is greater than the square of the third side.

A measure of the amount of rotation when either of two intersecting lines overlaps the other. Rotation is on the plane of two straight lines and around the intersection. Angle is the unit of measuring angle, and the symbol is 0. A fillet is divided into 360 equal parts, and each part is defined as 1 degree (1 degree).

Use the number 360, 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.