e 11-12 If u is a unit vector, find u . v and u . w. 11. 12. U u V W W 13. (a) Show that i . j = j . k = k . i = 0. (b) Show that i . i = j . j = k . k = 1. 14. A street vendor sells a hamburgers, b hot dogs, and c soft drinks on a given day. He charges $4 for a hamburger, $2.50 for a hot dog, and $1 for a soft drink. If A = (a, b, c) and P = (4, 2.5, 1), what is the meaning of the dot product A . P? 15-20 Find the angle between the vectors. (First find an exact expression and then approximate to the nearest degree.) 14 15. a - (4, 3), b = (2, -1) 16. a - (-2, 5), b = (5, 12)