course Mth 151 O™ÙãâŒj®Ãè¬x½Õäì™Â°ýŒâ¼Õýassignment #003
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11:19:25 Query 2.3.15 (Y ^ Z')U X, univ={a,..g}, X={a,c,e,g}, Y = {a,b,c}, Z = {b, ..., f} What is the set (Y ^ Z')U X?
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RESPONSE --> THIS IS QUESTION 19 IN OUR BOOK~ NOT ONE OF OUR ASSIGNED PROBLEMS Question 19: ({a,b,c} ^ {a,g}) U X = {a} U X = {a,c,e,g} confidence assessment: 3
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11:19:48 **Z' = {a,g}, the set of all elements of the universal set not in Z. Y ^ Z' = {a}, since a is the only element common to both Y and Z'. So (Y ^ Z') U X = {a, c, e, g}, the set of all elements which lie in at least one of the sets (Y ^ Z') U X. **
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RESPONSE --> I got this correct self critique assessment: 3
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11:22:26 Give the intersection of the two sets Y and Z'
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RESPONSE --> It does not list the # of this question, so I am assuming that we are still using the previous set information: U = {a,b,c,d,e,f,g} Y = {a,b,c} Z = {b,c,d,e,f} Y ^ Z' = {a,b,c} ^ {a,g} = {a} confidence assessment: 3
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11:22:36 **Z' = {a,g}, the set of all elements of the universal set not in Z. Y ^ Z' = {a}, since a is the only element common to both Y and Z'.**
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RESPONSE --> correct answer self critique assessment: 3
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11:23:49 Query 2.3.30 describe in words (A ^ B' ) U (B ^ A')
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RESPONSE --> confidence assessment: 0
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11:25:35 ** a description, not using a lot of set-theoretic terms, of (A ^ B' ) U (B ^ A') would be, all the elements that are in A and not in B, or that are not in A and are in B Or you might want to say something like 'elements which are in A but not B OR which are in B but not A'. STUDENT SOLUTION WITH INSTRUCTOR COMMENT:everything that is in set A and not in set B or everything that is in set B and is not in set A. INSTRUCTOR COMMENT: I'd avoid the use of 'everything' unless the word is necessary to the description. Otherwise it's likely to be misleading. **
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RESPONSE --> okay, I understand. I was making this more difficult than it really is. All the elements that are in A and not in B. All elements that are in B and not in A. self critique assessment: 2
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11:25:56 2.3.51 always or not always true: n(A U B) = n(A)+n(B)
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RESPONSE --> not always true confidence assessment: 2
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11:27:10 ** This conclusion is contradicted by many examples, including the one of the dark-haired and bright-eyed people in the q_a_. Basically n(A U B) isn't equal to n(A) + n(B) if there are some elements which are in both sets--i.e., in the intersection. } MORE DETAIL: The statement can be either true or false, depending on the sets A and B; it is not always true. The statement n(A U B) = n(A)+n(B) means that the number of elements in A U B is equal to the sum of the number of elements in A and the number of elements in B. The statement would be true for A = { c, f } and B = { a, g, h} because A U B would be { a, c, f, g, h} so n(A U B) = 5, and n(A) + n(B) = 2 + 3 = 5. The statement would not be true for A = { c, f, g } and B = { a, g, h} because A U B would be the same as before so n(AUB) = 5, while n(A) + n(B) = 3 + 3 = 6. The precise condition for which the statement is true is that A and B have nothing in common. In that case n(A U B) = n(A) + n(B). A more precise mathematical way to state this is to say that n(A U B) = n(A) + n(B) if and only if the intersection A ^ B of the two sets is empty. **
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RESPONSE --> correct answer. it depends on the sets A and B whether the statement is true or false. self critique assessment: 3
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11:29:57 06-08-2007 11:29:57 Query 2.3.60 X = {1,3,5}, Y = {1,2,3}. Find (X ^ Y)' and X' U Y'.
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NOTES -------> (X ^ Y)' = ({1,3,5} ^ {1,2,3}' = {2,4} ^ {4,5} = {4} X' U Y' = {2,4} ^ {4,5} = {2,4,5}
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11:34:54 ** X ^ Y = {1,3} so (X ^ Y) ' = {1,3}' = {2, 4, 5}. (X ' U Y ' ) = {2, 4} U {4, 5} = {2, 4, 5} The two resulting sets are equal so a reasonable conjecture would be that (X ^ Y)' = X' U Y'. **
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RESPONSE --> ok, I got part b correct but not part a. But I now understand part a. I had broken it down individually in the ( ) rather than the whole set. self critique assessment: 3
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11:41:11 2.3.72 A = {3,6,9,12}, B = {6,8}.
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RESPONSE --> Find A X B and B X A A X B = {(3,6), (3,8), (6,6), (6,8), (9,6), (9,8), (12,6), (12,8)} B X A = {(6,3), (6,6), (6,9),(6, 12), (8,3), (8,6), (8,9), (8,12)} confidence assessment: 3
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11:41:28 ** (A X B) = {(3,6),(3,8),(6,6),(6,8),(9,6),(9,8),(12,6), (12,8)} (B X A) = (6,3),(6,6),(6,9),(6,12),(8,3),(8,6),(8,9),(8,12)} How is n(A x B) related to n(A) and n(B)? n(S) stands for the number of elements in the set S, i.e., its cardinality. n(A x B) = n(A) * n(B) **
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RESPONSE --> correct answer self critique assessment: 3
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11:43:01 2.3.84 Shade A U B
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RESPONSE --> WHERE ARE THE DRAWING TOOLS TO DRAW AND SHADE A VENN DIAGRAM?? confidence assessment: 3
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11:43:52 ** everything in A and everything in B would be shaded. The rest of the universal set (the region outside A and B but still in the rectangle) wouldn't be. **
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RESPONSE --> ohhhh. I see, I need to just explain in words what I would and would not shade. i understand. self critique assessment: 3
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11:45:46 Query 2.3.100 Shade (A' ^ B) ^ C
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RESPONSE --> The section of A circle and B circle that overlap would be shaded and the section of the cirlces A,B,C that overlap each other would be shaded. confidence assessment: 2
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11:47:10 ** you would have to shade every region that lies outside of A and also inside B and also inside C. This would be the single region in the overlap of B and C but not including any part of A. Another way to put it: the region common to B and C, but not including any of A **
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RESPONSE --> oops. I answered problem 101 instead of 100. self critique assessment: 3
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12:02:53 Describe the shading of the set (A ^ B)' U C.
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RESPONSE --> Everything that is not A and not B, and the part of C that does not include A or B confidence assessment: 2
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12:04:44 2.3.114 Largest area of A shaded (sets A,B,C). Write a description using A, B, C, subset, union, intersection symbols, ', - for the shaded region.
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RESPONSE --> ? confidence assessment: 0
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12:06:14 ** Student Answer and Instructor Response: (B'^C')^A Instructor Response: Good. Another alternative would be A - (B U C ), and others are mentioned below. COMMON ERROR: A ^ (B' U C') INSTRUCTOR COMMENT: This is close but A ^ (B' U C') would contain all of B ^ C, including a part that's not shaded. A ^ (B U C)' would be one correct answer. **
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RESPONSE --> ok, still having a little trouble with this. I am working through extra problems in the book for practice. self critique assessment: 2
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