Hat is the approximate distance between portland, oregon (45° north, 122° west), and san francisco, california (37° north, 122° west). use 3,960 miles for the radius of earth

Since both places are on the same longitude (122° west) and different lattitudes 45° north and 37° north, the distance between the two place lies on a great circle (along a line of longitude). Difference in latitudes = 45 - 37 = 8° (subtract the lattitudes because both sides are on the same side in the latitude i.e. both are north) The distance between two points along the line of longitude is given by theta / 360 x 2 x pi x R: where theta = 8° and R is the radius of the earth = 3,960 miles. d = 8 / 360 x 2 x pi x 3960 = 552.9 miles