There are four corners on the cover of a math textbook, and each corner has a vertex and two sides. According to the meaning of an angle, the figure composed of two rays drawn from a point is called an angle, this point is called the vertex of the angle, and these two rays are called the edges of the angle.

The cover of a math textbook is a rectangle with four corners. Answer accordingly. The purpose of this exam is to understand the significance of mastering the angle, the names and applications of each part of the angle.

A rectangle, also called a rectangle, is a plane figure, but it is a parallelogram with right angles. A rectangle is also defined as a parallelogram with four corners at right angles. A square is a special rectangle with four sides of the same length.

The essence of a rectangle is: two diagonal lines are equal; Two diagonal lines are equally divided; Two groups of opposite sides are parallel respectively; The two groups of opposite sides are equal respectively; All four corners are right angles; There are two symmetrical axes (there are four squares); Unstable (easily deformed); The square of the diagonal length of a rectangle is the sum of the squares of both sides; The quadrilateral obtained by connecting the midpoints of the sides of the rectangle in turn is a diamond.

Determination of rectangle:

1. A parallelogram with right angles is a rectangle.

2. Parallelograms with equal diagonals are rectangles.

3. A parallelogram with adjacent sides perpendicular to each other is a rectangle.

A quadrilateral with three right angles is a rectangle.

5. Quadrilaterals with equal diagonals and bisecting each other are rectangles.