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Question 38 (iii) - Choice (A) If the angle of elevation from Shreya’s eye changes from 45° to 30°, when she moves some distance back from the original position. Find the distance she moves back. Note: She moves back, so she is going from left to right We need to find distance HF Also, by symmetry HF = GE In right angle triangle AGC tan G = (𝑆𝑖𝑑𝑒 𝑜𝑝𝑝𝑜𝑠𝑖𝑡𝑒 𝑡𝑜 𝑎𝑛𝑔𝑙𝑒" " 𝐺)/(𝑆𝑖𝑑𝑒 𝑎𝑑𝑗𝑎𝑐𝑒𝑛𝑡 𝑡𝑜 𝑎𝑛𝑔𝑙𝑒" " 𝐺) tan G = AC/𝐺𝐶 tan 30° = 41/GC 1/√3 = 41/GC GC = 41 √𝟑 In right angle triangle AEC tan E = (𝑆𝑖𝑑𝑒 𝑜𝑝𝑝𝑜𝑠𝑖𝑡𝑒 𝑡𝑜 𝑎𝑛𝑔𝑙𝑒" " 𝑆)/(𝑆𝑖𝑑𝑒 𝑎𝑑𝑗𝑎𝑐𝑒𝑛𝑡 𝑡𝑜 𝑎𝑛𝑔𝑙𝑒" " 𝑆) tan E = 𝐴𝐶/𝐸𝐶 tan 45° = 𝐴𝐶/𝐸𝐶 1 = 41/𝐸𝐶 EC = 41 Now, GC = GE + EC Putting values 41√𝟑 = GE + 41 41√3 – 41 = GE 41 (√3 – 1) = GE GE = 41 (√𝟑 – 1) m ∴ The distance she moved back = 41 (√𝟑 – 1) m

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 15 years. He provides courses for Maths, Science and Computer Science at Teachoo