As shown in the figure, Xiaohong wants to measure the height of a big tree 30 meters away from A. She stands at A and looks up at the top of tree B. The altitude of tree B is 30 (that is, ∠ BDE=30). Know that Xiaohong is 1.52m, and find the height of the big tree. Solution: ∫∠BDE = 30, DE = 30.
∴BE= 10√3≈ 17.32
∴BC= 18.84