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The angle of elevation of the top of a pole from a point A on the ground is 30°. The angle of elevation changes to 45°, after moving 20 meters towards the base of the pole. Then the height of the pole, in meters, is

Solution

✅ Correct Option: 4

Let the height of the pole be hh and the distance from the second point (where angle =45°= 45°) to the base of the pole be dd.


From the second point (after walking 20 m toward the pole):

tan⁡45°=hd\tan 45° = \dfrac{h}{d}

1=hd1 = \dfrac{h}{d}

d=hd = h

💡 Since tan⁡45°=1\tan 45° = 1, the height and base distance from this point are equal.


From point A, the total base distance =20+d=20+h= 20 + d = 20 + h

tan⁡30°=h20+h\tan 30° = \dfrac{h}{20 + h}

13=h20+h\dfrac{1}{\sqrt{3}} = \dfrac{h}{20 + h}

Cross-multiplying:

20+h=3⋅h20 + h = \sqrt{3} \cdot h

20=3⋅h−h20 = \sqrt{3} \cdot h - h

20=h(3−1)20 = h(\sqrt{3} - 1)

h=203−1h = \dfrac{20}{\sqrt{3} - 1}


Rationalizing the denominator (multiplying top and bottom by 3+1\sqrt{3} + 1 to remove the square root from the denominator):

h=203−1×3+13+1h = \dfrac{20}{\sqrt{3} - 1} \times \dfrac{\sqrt{3} + 1}{\sqrt{3} + 1}

h=20(3+1)(3)2−(1)2h = \dfrac{20(\sqrt{3} + 1)}{(\sqrt{3})^2 - (1)^2}

h=20(3+1)3−1h = \dfrac{20(\sqrt{3} + 1)}{3 - 1}

h=20(3+1)2h = \dfrac{20(\sqrt{3} + 1)}{2}

h=10(3+1) meters\boxed{h = 10(\sqrt{3} + 1) \text{ meters}}

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