We need to find the point of intersection of the curves f_{1}(x) = cos^{-1}(cos x) and f_{2}(x) = 10 - x/10 in the domain [0, 4*π*].

f_{1}(x) is a period function with period 2*π* and f_{2}(x) is a straight line plotting both graphs

Therefore, A, B and C are the points of intersection of both curves which obviously satisfy the given equations, hence there are three such points.