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A plane mirror is placed flat on the ground, 60 m away from the base of a tower. From the eye, the top of the tower and its image formed in the mirror are seen under a right angle. What is the height of the tower?
- 30 m
- 60 m
- 90 m
- 120 m
Correct answer: 30 m
Solution
For a plane mirror on the ground, the image of the tower is as far below the ground as the tower is above it. The eye sees the top and its image at right angles, which gives a right triangle with the mirror distance as one side. Using the geometry, the tower height comes out to 30 m.
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