Prove that the three triangles are congruent. Write down the formula for calculating the area of rectangles that are displayed by numbers. Move the point D up. Then move down points E and F. Did the rectangular areas change? Now write a new formula for the area of resulting ​​squares. Write the equality between the sum of these rectangular areas at the beginning and at the end. Move points A, B and C at some new positions. Then repeat the previous procedure. What do you conclude?