At latitude 15° N, a city lies at 70° E longitude. Another city lies at 80° E longitude on the same parallel. Calculate the approximate east‑west distance between these two cities. Assume the Earth’s radius is 6371 km and use the formula $d=Rcosphi,Deltalambda$, where angles are in radians.

Step-by-step solution

1. 1. Find the difference in longitude: $Deltalambda=80°-70°=10°$.
2. 2. Convert $Deltalambda$ to radians: $10°\times \frac{\pi }{180}=0.17453$ rad.
3. 3. Compute $cosphi$ where $phi=15°$: $cos15°approx0.96593$.
4. 4. Multiply: $d=6371\times 0.96593\times 0.17453$. First compute $6371\times 0.96593\approx 6157$ km.
5. 5. Then $6157\times 0.17453\approx 1075$ km.
6. 6. Thus the east‑west distance is about 1075 km.

Concept tested: East‑west distance along latitude

Published 1 October 2026 · How this solution was prepared and checked