Question 1148544
It seems A and B are two points on surface of Earth and C is the centre of the Earth.


Let us consider Earth to be a perfect sphere.


AC = BC = Radius = 4000
AB = 700

Suppose, angle <ACB = &theta;

Using Cosine rule in triangle ABC
{{{c^2 = a^2 + b^2 - 2*a*b*cos (theta)}}}
{{{700^2 = 4000^2 + 4000^2 - 2*4000*4000*cos (theta)}}}
{{{cos (theta) = (2*4000^2 - 700^2)/(2*4000^2)}}}
{{{cos (theta) = 1 - 7^2/(2*40^2) = 1 - 49/3200 = 0.9847}}}
{{{ theta = ArcCos(0.9847) = 0.1752}}} radians