18. a. Verify that the vectors a = (2, 5, -1 ) and b = (3, - 1, 1 ) are perpendicular. b. Find the direction cosines for each vector. c. If m = (cos aa, cos Ba, Cos ya), the direction cosines for a, and if m2 = (cos ab, cos Bb, Cos Yb), the direction cosines for b2, verify that mj . m2 = 0