This teaching aid is used to explore Pythagorean theorem. Take three sides of the right triangle ABC as sides and make squares A, B and C outward; Among them, Figure B is divided into three parts: ①, ② and ③, such as the teaching aid diagram. The area of Figure A is, the area of Figure B is and the area of Figure C is. Inserting Figures ①, ②, ③ and C into Figure A just fills the whole Figure A ... That is to say, the sum of the areas of Figures ①, ②, ③ and C is equal to the area of Figure A, that is, the sum of the areas of Figures B and C is equal to the area of Figure A, so there is the Pythagorean theorem.