(P1.20)-(a) Prove that P = cos u1ax 1 sin u+ay and Q = cos u2ax + sin u2ay are unit vectors in the xy-plane, respectively, making angles u1 and u2 with the x-axis.
(b) By means of dot product, obtain the formula for cos1u2 2 u1 2. By similarly formulating P and Q, obtain the formula for cos1u2 + u1.
(c) If u is the angle between P and Q, find 1/2 P - Q in terms of u.
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