# How do you caluclate the length of the 40 degree paralel of latitude, to the nearest 10 km?

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• Anonymous

If r is the equatorial radius of earth, the radius of the 40 deg. parallel of latitude is:

r cos(40 deg).

Its circumference is 2pi r cos(40).

Using r = 6,378.137 km (Wikipedia) gives:

2 pi 6378.137 cos(40)

= 30699.24 km

= 30700 km to nearest 10km.