The line segment connecting any two points on a circle is called a chord, and the chord passing through the center of the circle is called a diameter, which is the longest chord in the circle.

Theorem of intersecting chords of a circle: the product of two intersecting chords in a circle is equal to the length of two straight lines divided by the intersection point. Draw two chords through a point in a circle, and the product of two line segments divided by the point is equal.

The hypotenuse of a right triangle. The sum of squares of the sides of two right angles (short hook and long strand) is equal to the square of the side length of the hypotenuse (chord).

In a right-angled triangle on the plane, the square of the length of two right-angled sides adds up to the square of the length of the hypotenuse. If the lengths of two right-angled sides of a right-angled triangle are A and B, respectively, and the length of the hypotenuse is C, then it can be expressed in mathematical language as: A? +b？ =c？ ,

Pythagorean theorem is a special case of cosine theorem.