course assignment #013013. Negation
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11:36:03 `q001. There are 4 questions in this set. Two statements are said to be negations of one another if exactly one of the statements must be true. This means that if one statement is true the other must be false, and if one statement is false the other must be true. What statement is the negation of the statement 'all men are over six feet tall'?
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RESPONSE --> Not all men are over six feet tall. confidence assessment: 2
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11:37:59 You might think that the negation would be 'no men are over six feet tall'. However, the negation is in fact 'some men are not over 6 feet tall'. The negation of a statement, in addition to being false whenever the statement is true, has to include every possibility except those covered by the statement itself. With respect to men being over six feet tall, there are three possibilities: 1. All men are over six feet tall, 2. no men are over six feet tall, and 3. some men are over six feet tall while others aren't. It should be clear that statements 1 and 2 do not cover the possibility of the third. In fact no two of these statements cover the possibility of the remaining one. However the following two statements do cover all possibilities: All men are over six feet tall (the original statement), and some men are not over six feet tall. The second statement might seem to be identical to statement 3, 'some men are over six feet tall while others aren't', but it is not. The statement 'some men are not over six feet tall' does not address whether there are men over six feet tall or not, while statement 3 states that there are. And the statement 'some men are not over six feet tall' might seem to leave out the possibility of statement 2, 'no men are over six feet tall', but again it doesn't address whether or not there are also men over six the tall. Therefore the negation of the statement 'all men are over six feet tall' is 'some men are not over six feet tall'.
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RESPONSE --> self critique assessment: 3
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11:41:50 In the given problem the negation 'some men are under 6 ft tall' is true, proving that the original statement 'all men are over 6 ft tall' is false.
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RESPONSE --> When using the word all you need to substitute the word some in order to cover every possibility. Some men are under 20 feet tall would be All men are under 20 feet tall. self critique assessment: 3
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11:43:28 These examples demonstrate why it is important to figure out the negation before you even thing about which statement is true. Either the statement or its negation will be true, but never both.
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RESPONSE --> A statement or the negation will be true but not both. Figure out the negation before trying to figure out which statement is true. self critique assessment: 3
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11:43:57 `q002. What is the negation of the statement 'some men are over six feet tall' ?
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RESPONSE --> All men are over six feet tall confidence assessment: 3
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11:46:46 While it might seem that the negation of this statement is 'some men are not over six feet tall', the correct negation is 'no men are over six feet tall'. This is because there is an 'overlap' between 'some men are over six feet tall' and 'some men are not over six feet tall' because both statements are true if some men are over six feet while some are under six feet. Negations have to be exact opposites--if one statement is true the other must be false--in addition to the condition that the two statements cover every possible occurance. Again we have the three possibilities, 1. All men are over six feet tall, 2. no men are over six feet tall, and 3. some men are over six feet tall while others aren't. The statement ' some men are over six feet tall' is consistent with statements 1 and 3, because if all men are over six feet tall then certainly some men are over 6 feet tall, and if some men are over 6 feet tall and others aren't, it is certainly true that some men are over six feet tall. The only statement not consistent with 'some men are over six feet tall' is Statement 2, 'No men are over six feet tall'. Thus this statement is the negation we are looking for.
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RESPONSE --> I needed to write no men are over six feet tall because some would imply that one or more would be over six feet. Therefore I needed to put no men and that would cover everyone. self critique assessment: 2
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11:55:00 `q003. As seen in the preceding two questions, the negation of a statement that says 'all are' or 'all do' is 'some aren't' or 'some don't', and the negation of a statement that says 'some are' or 'some do' is 'all aren't' or 'none are', or 'all do not' or 'none do'. Each of the following statements can be expressed as and 'all' statement or a 'some' statement. Identify which is which and give the negation of each statement: 1. Every dog has its day. 2. Some roses are black. 3. Every attempt fails. 4. In some cases the desired outcome isn't attained.
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RESPONSE --> 1 is an all statement. Some dogs dont have their day. 2 is a some statement. All roses are not black. 3. is an all statement. Some attempts do not fail. 4.is a some statement. In all cases the desired outcome is attained. confidence assessment:
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11:56:15 Statement 1 can be expressed as 'All dogs do have their day', a form of 'all do'. The negation of 'all do' is 'some don't'. In this case the negation might be expressed as 'some dogs do not have their day'. Statement 2 is a straightforward 'some are' statement having negation 'all are not', expressed in this case as 'no roses are black', or equivalently 'there are no black roses'. Statement 3 can be restated equivalently in 'all do' form as 'all attempts do fail', and is negated in 'some don't' form as 'some attempts do not fail', or equivalently as 'some attempts succeed'. Statement 4 can be equivalently expressed in 'some are' form as 'some outcomes are not as desired'. This statement is negated by the 'none are' form as 'no outcomes are not as desired', which can then be expressed as 'all outcomes are as desired'.
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RESPONSE --> I think I understand now self critique assessment: 3
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11:59:26 `q004. Negate the following statements: 1. No roses are black. 2. Some roses are not black. 3. There were Dodo birds that weren't stupid. 4. There were never turtles that weren't slow.
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RESPONSE --> Some roses are black. All roses are black. All Dodo birds were stupid. There were some turtles that weren't slow. confidence assessment: 3
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12:00:12 Statement 1 says that there is no such thing as a rose which is not black, which says that all roses fail to be black. The negation of 'all are' is 'some aren't', so the negation of 'all roses are not black' is 'some roses are not not black', which is the same as 'some roses are black'. Statement 2 is a 'some are' statement, negated in the 'all are not' form by 'all roses are not not black', or equivalently, 'all roses are black'. Statement 3 is equivalent to saying that 'some Dodos birds were not stupid', negated as 'all are not' in the form 'all Dodo birds were not not stupid', or equivalently as 'all Dodo birds were stupid'. Statement 4 is equivalent of saying that 'all turtles were slow', equivalent of the 'all are' form. This is negated in 'some are not' form by 'some turtles were not slow'.
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RESPONSE --> self critique assessment: 3
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assignment 14 wƳݟ܌y{` assignment #014 014. Truth Tables Liberal Arts Mathematics I 10-02-2008
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12:07:52 `q001. There are 8 questions in this set. If each of the propositions p and q can be either true or false, what combinations of truth values are possible for the two propositions (e.g., one possibility is that p is false and q is true; list the other possibilities)?
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RESPONSE --> if p is false q is true if p is false q is false if p is true q is true if p is true q is false confidence assessment: 3
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12:08:16 It is possible that p is true and q is true. Another possibility is that p is true and q is false. A third possibility is that p is false and q is true. A fourth possibility is that p is false and q is false. These possibilities can be listed as TT, TF, FT and FF, where it is understood that the first truth value is for p and the second for q.
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RESPONSE --> self critique assessment: 3
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12:11:00 `q002. For each of the for possibilities TT, TF, FT and FF, what is the truth value of the compound statement p ^ q ?
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RESPONSE --> if p and q are true p^q is T if p is true and q is false p^q is F if p is false and q is true p^q is F if p is false and q is false p^q is F confidence assessment: 3
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12:11:07 p ^ q means 'p and q', which is only true if both p and q are true. In the case TT, p is true and q is true so p ^ q is true. In the case TF, p is true and q is false so p ^ q is false. In the case FT, p is false and q is true so p ^ q is false. In the case FF, p is false and q is false so p ^ q is false.
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RESPONSE --> self critique assessment: 3
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12:13:32 `q003. Write the results of the preceding problem in the form of a truth table.
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RESPONSE --> p and q p q p^q T T T T F F F T F F F F confidence assessment: 3
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12:13:40 The truth table must have headings for p, q and p ^ q. It must include a line for each of the possible combinations of truth values for p and q. The table is as follows: p q p ^ q T T T T F F F T F F F F.
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RESPONSE --> self critique assessment: 3
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12:17:58 `q004. For each of the possible combinations TT, TF, FT, FF, what is the truth value of the proposition p ^ ~q?
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RESPONSE --> p^~q is p is true q is true p^q~ is F p is true q is false p^q~ is T p is false q is true p^q~ is F p is false q is false p^q~ is F confidence assessment: 3
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12:18:33 For TT we have p true, q true so ~q is false and p ^ ~q is false. For TF we have p true, q false so ~q is true and p ^ ~q is true. For FT we have p false, q true so ~q is false and p ^ ~q is false. For FF we have p false, q false so ~q is true and p ^ ~q is false.
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RESPONSE --> self critique assessment: 3
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12:22:01 `q005. Give the results of the preceding question in the form of a truth table.
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RESPONSE --> p^q~ p q ~q p^q~ T T F F T F T T F T F F F F T F confidence assessment: 3
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12:22:08 The truth table will have to have headings for p, q, ~q and p ^ ~q. We therefore have the following: p q ~q p^~q T T F F T F T T F T F F F F T F
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RESPONSE --> self critique assessment: 3
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12:26:52 `q006. Give the truth table for the proposition p U q, where U stands for disjunction.
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RESPONSE --> pUq means p or q or both p q pUq T T T T F T F T T F F F confidence assessment: 3
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12:27:10 p U q means 'p or q' and is true whenever at least one of the statements p, q is true. Therefore p U q is true in the cases TT, TF, FT, all of which have at least one 'true', and false in the case FF. The truth table therefore reads p q p U q T T T T F T F T T F F F
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RESPONSE --> I under stand self critique assessment: 3
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12:32:17 `q007. Reason out the truth values of the proposition ~(pU~q).
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RESPONSE --> p q ~q pU~q ~{pU~q} T T F T F T F T T F F T F F T F F T T F confidence assessment: 3
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12:33:06 In the case TT p is true and q is true, so ~q is false. Thus p U ~q is true, since p is true. So ~(p U ~q) is false. In the case TF p is true and q is false, so ~q is true. Thus p U ~q is true, since p is true (as is q). So ~(p U ~q) is false. In the case FT p is false and q is true, so ~q is false. Thus p U ~q is false, since neither p nor ~q is true. So ~(p U ~q) is true. In the case FF p is false and q is false, so ~q is true. Thus p U ~q is true, since ~q is true. So ~(p U ~q) is false.
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RESPONSE --> self critique assessment: 3
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12:36:59 `q008. Construct a truth table for the proposition of the preceding question.
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RESPONSE --> p q ~q pU~q ~{pU~q} T T F T F T F T T F F T F F T F F T T F confidence assessment: 3
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12:37:35 We need headings for p, q, ~q, p U ~q and ~(p U ~q). Our truth table therefore read as follows: p q ~q pU~q ~(pU~q) T T F T F T F T T F F T F F T F F T T F
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RESPONSE --> self critique assessment: 3
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