What angle would Eratosthenes have measured had the World been flat?

Explanation:

Angle FEA =  angle ECG (alternate angles).

Angle GCD = 180o – x (supplementary angles)

→ angle CDB          = 180o – (angle GCD + angle CGD)  (Angles in a triangle)

→ angle CDB = 180o – (180o – x + y) =  x – y

→ arc AB subtends angle (x – y) at the Earth’s centre.

→ 1o subtends arc of    AB ÷  (x – y) miles

→  Earth’s circumference  =  360 x  AB ÷ (x – y)  miles

=  360 x  580 ÷  7.2  miles   = 29000 miles (statute miles).

its a 5.5 n

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