Problem description:

In other words, it is proved that this problem is similar to the conditions after ∵∴, such as ∴AB‖CD (the same angle is equal and two straight lines are parallel).

I gave an example of the condition in brackets, and there are many others. Please help me. Thank you.

Analysis:

I'll do it.

Two triangles with equal angles are similar.

Two figures in proportion on both sides are similar.

Two triangles with proportional sides and equal included angles are similar.

A triangle with two equal angles and a side length of 1

A triangle with two equal sides is congruent.

The distance from the intersection point of the bisector of a triangle to the three sides is equal.

The distance from the intersection of the perpendicular lines of three sides of a triangle to each vertex of the triangle is equal.

The obtuse angle formed by the intersection of bisectors of two corners of a triangle is 90 degrees+half of the third triangle.

The included angle of the line perpendicular to the waist of the isosceles triangle is half of the vertex angle.

Draw a straight line through the diagonal intersection of the parallelogram, and divide the parallelogram into two congruent figures.

The diagonal sum of the quadrilateral formed by any four points on a circle is equal to 180 degrees.

The center line of the hypotenuse of a right triangle is equal to half of the hypotenuse.

If a right triangle has an angle of 30 degrees, its opposite side is equal to half of the hypotenuse.