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MATHEMATICS 226, FALL 2014, PROBLEM SET 11 Due on Friday, September 12 Write clearly and legibly, in complete sentences. You must provide complete explanations for all your solutions; answers without justification, even if correct, will not be marked. You may discuss the homework with other students, but the final write-up must be your own. 1. (10 marks) Specify the boundary and the interior of the sets S in 3space whose points (x, y, z) satisfy the given conditions. Is S open, closed, or neither? (a) x2 + y 2 + z 2 ≥ 16 (b) z ≥ 0, x2 + (y − 2)2 + z 2 < 1 2. (10 marks) Find all values of t for which the vector v = 4ti − tj + 6k is perpendicular to the vector w = 2i + (4 − 2t)j + (1 − 2t)k. 3. (10 marks) Find vectors a, b, c in R2 such that the set of points whose position vector r satisfies the inequalities r · a ≤ 1, r · b ≤ 1, r · c ≤ 1 is the triangle with vertices (1, 2), (2, −2), (−3, 0). 4. (10 marks) Find two unit vectors each of which makes equal angles with the vectors u = 4i − j − k, v = i + j, and w = 2i + j + k. 1 c Laba. Not to be copied, used, or revised without explicit written permission from I. the copyright owner. 1