Horizon

The top of a lighthouse is 19 m above the sea. How far away is an object which is just "on the horizon"? [Assume the Earth is a sphere of radius 6378.1 km.]

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Pythagorean theorem is the base for the right triangle calculator.
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You need to know the following knowledge to solve this word math problem:

solid geometry
sphere
planimetrics
Pythagorean theorem
right triangle
circle
triangle
8th grade (13y)
9th grade (14y)
high school

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