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(b) How would you define the Euclidean length of the “diagonal” of the box in part (a)?

Figure Ex-33

34.
         (a) Suppose that u and v are vectors in . Show that

(b) The result in part (a) states a theorem about parallelograms in . What is the theorem?

35.                                                           and , then
         (a) If u and v are orthogonal vectors in such that
              _________ .

         (b) Draw a picture to illustrate this result.

In the accompanying figure the vectors u, v, and  form a triangle in , and denotes the

36. angle between u and v. It follows from the law of cosines in trigonometry that

Do you think that this formula still holds if u and v are vectors in ? Justify your answer.

                                                  Figure Ex-36

          Indicate whether each statement is always true or sometimes false. Justify your answer by giving
37. a logical argument or a counterexample.
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