6. (10 pts) recall the cosine formula: if a triangle has side lengths a, b and c, and the angle between the sides of length a and b is e, then c^2 = a^2 +b^2+2ab cose. (a) restate the cosine formula as a statement about vectors v and w with angle 8 between them. (b) use what you know about dot products to prove the above formulation of the cosine formula