Interpolationsparabel

A = (1, 2)
B = (3, 3)
C = (4, 1)
l1(x) = (x - x(B)) * (x - x(C))
l2(x) = (x - x(A)) * (x - x(C))
l3(x) = (x - x(A)) * (x - x(B))
c_1: y(A) / l1(x(A))
c_2: y(B) / l2(x(B))
c_3: y(C) / l3(x(C))
p(x) = c_1 * l1(x) + c_2 * l2(x) + c_3 * l3(x)
a = false