Longitude problem on a Terrestrial Sphere

[Equilibrium]

Homework Statement

How far apart (in miles) are 2 points on the equator if their longitudes differ by 1 degree?
The correct answer is 69.8 miles, I'm not sure if typo

Homework Equations

$$S=r\theta$$
radius of Earth = 3959 miles

The Attempt at a Solution

$$\theta = 1\deg*\frac{\pi}{180}$$
$$S=3959*\frac{\pi}{180}$$
$$S = 69.1 miles$$

 

[Curious3141]

Nothing wrong with your working, except that you should be more clear that you're starting by converting theta into radian measure. But your answer is right.

The difference could be because of the value you're supposed to use for the Earth's equatorial (great circle) radius. Are you given a value you're supposed to use?

The value you quoted looks quite OK, but google's is slightly different: 3 963.1676 miles, and yields a slightly different answer (69.2mi, still closer to yours than the expected one).

 

[Equilibrium]

thanks for verifying