2 Consider a triangle ABC and let D be a point on the line between A and B. Use thedot product to prove that|−→AC|2|−−→BD| + |−−→BC|2|−−→AD| − |−−→CD|2|−→AB| = |−→AB||−−→AD||−−→BD|.Hint: You may find it helpful to write everything in terms ofx =−−→AD, y =−−→DC, z =−−→BDusing the identities−→AC =−−→AD +−−→DC and −−→BC =−−→BD +−−→DC.