As shown in the figure, the triangle abc is a right triangle, the length of ab is 20 cm, and the shadow 1 is 7 cm larger than the shadow 2. Find the length of BC. Hurry up and adopt it! !

Connect B and AC with the intersection D of the circle, and let AD be x, x and CD be y.. Then BD is XY, BC is XY+X, and according to Pythagorean theorem, AC =AB +BC, that is, (X+Y) = 20+xy+X. The shadow 1 is 7 larger than 2, and the area of the semicircle is 7 larger than that of the triangle (plus the overlapping area of the triangle and the circle), that is, 1/2* derivative * 10 square-1/2 * 20 * root sign (XY+X square) = 7. The equations are solved by two equations, X=Y=, so BC= root sign (XY+X square) =, and you can do the math yourself.