Find the height of a tree when it is found that on walking away from it 20 m, in a horizontal line through its base, the elevation of its top changes from 60° to 30°.
Let AB be the tree of height h m .
Let the two points be C and D such that CD = 20 m, ∠ADB = 30° and ∠ACB = 60°
Hence, height of the tree is 17.32 m.
