"If it flies directly" means that it will fly a great circle route.

Here's the route (London is at the bottom of the image, Los Angeles at the top):

London to Los Angeles great circle route

Image from Google Earth.

We learned above that the latitude and longitude for London and Los Angeles are as follows:

London: φ1 = 51°32' N = 0.899426,

λ1 = 0° 5' W = −0.001454

Los Angeles: φ2 = 34° 3' N = 0.594285,

λ2 = 118° 14' W = −2.063561

Applying the formula for the central angle gives:

Central angle =

`2 arcsin sqrt( sin^2 ((-0.305)/2) +cos (0.899) cos (0.594) sin^2 ((-2.062)/2) )`

= 1.374296 (full calculator accuracy was used throughout)

So the distance between London and Los Angeles is:

s = = 6371 × 1.374296 = 8756 km

Please support IntMath!