What is exercise 1 in mathematics book p16-17 3. As shown in the figure, Xiaohong wants to measure the height of the big tree 30m away from A. she stands at a and looks up at the top of the tree B, with an elevation of 30 ° (i.e. ∠ BDE = 30 °). Given that Xiaohong is 1.52m tall, she can calculate the height of the big tree (the result is accurate to 0.1M)

The right side of a right triangle at 30 degrees is half of the hypotenuse
Known: de = 30m ∠ BDE = 30 °
Let be = XM, then BD = 2XM
x²+30²=（2x)²
X = 10 radical 3 = 17.3
BC=17.3+1.52=18.82=18.8m

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