Generally, these questions are not difficult. If you subtract the shadow falling on the wall from the height of the tree, the value is proportional to the shadow falling on the ground. According to this relationship, it is easy to get the height or shadow length of the tree. Maybe you will ask why the height of the tree minus the shadow on the wall is directly proportional to the shadow of the tree falling to the ground? You can take a look at a corresponding problem (it's too much trouble for me to draw here, so I won't do it, sorry! ), because sunlight is parallel lines, the quadrilateral formed by the points on the tree corresponding to the shadow top, shadow tail, tree top and shadow tail on the wall is a parallelogram. Because the opposite sides of the parallelogram are equal, subtracting the length of the shadow falling on the wall from the height of the tree is equivalent to that the tree is so much shorter and the shadow is so much shorter. Most importantly, the shadow falls right under the corner, which is simpler to calculate. Simplified to the formula: (height of tree-length of shadow falling on the wall)/length of shadow falling on the ground = total length of tree/total length of shadow.