Remember that quadrangles are squares, diamonds, parallelograms, isosceles trapeziums, trapeziums, rectangles and irregular quadrangles. There are also the properties of equilateral triangle, isosceles triangle and ordinary triangle. Use each other to prove it.

For example, an equilateral triangle has only one isosceles triangle.

Answer: Wrong, because all sides of an equilateral triangle are equal, so an equilateral triangle also belongs to a triangle with equal sides.

In this way, nature is used to give counterexamples to prove.

That's all for junior high school. In high school, the teacher will speak slowly. That's all you need to master.