MCQs / Mathematics / Logic
Logic MCQs — Mathematics (page 3) 64 multiple-choice questions on Logic from Mathematics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.
51. An axiom is a statement that is: shown false by an example believed true but not yet proved proved using other theorems accepted as true without proof Answer: D) accepted as true without proof
Explanation: Axioms (postulates) are the starting points of a mathematical system. SLO M-09-B-14 · Knowledge
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52. Pythagoras' result a^2 + b^2 = c^2 for right triangles is: an axiom a definition a conjecture a theorem Answer: D) a theorem
Explanation: It has been proved in many ways. SLO M-09-B-14 · Knowledge
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53. The expression n^2 + n + 41 is prime for n = 0, 1, 2, ldots, 39. For n = 40 its value is 1681 = 41^2. This shows that: 40 cases make a proof 1681 is prime the expression is always prime a pattern can fail even after many cases, so it needs a proof Answer: D) a pattern can fail even after many cases, so it needs a proof
Explanation: Forty examples worked, yet n = 40 is a counterexample. SLO M-09-B-13 · Knowledge
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54. The sum of an even number 2m and an odd number 2n + 1 is: 2(m + n), which is even 2(m + n) + 1, which is odd 2mn + 1 m + n + 1 Answer: B) 2(m + n) + 1, which is odd
Explanation: 2m + 2n + 1 = 2(m + n) + 1. SLO M-09-B-15 · Knowledge
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55. A statement that has been proved is called a: theorem hypothesis counterexample conjecture Answer: A) theorem
Explanation: Once proved, a statement becomes a theorem. SLO M-09-B-13 · Knowledge
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56. In geometry, the word postulate means the same as: conjecture axiom theorem lemma Answer: B) axiom
Explanation: Postulates are axioms of geometry. SLO M-09-B-14 · Knowledge
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57. A corollary is: a definition an axiom a result that follows directly from a theorem an unproved statement Answer: C) a result that follows directly from a theorem
Explanation: Example: from “angles of a triangle add to 180^circ” it follows that each angle of an equilateral triangle is 60^circ. SLO M-09-B-14 · Knowledge
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58. Which statement is an identity (true for every x)? x + 3 = 7 (x + 3)^2 = x^2 + 3x + 9 (x + 3)^2 = x^2 + 6x + 9 (x + 3)^2 = x^2 + 9 Answer: C) (x + 3)^2 = x^2 + 6x + 9
Explanation: Only (x + 3)^2 = x^2 + 6x + 9 holds for all x. SLO M-09-B-15 · Knowledge
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59. The sum of four consecutive integers n, n + 1, n + 2, n + 3 equals: 4(n + 1) 4n + 6 = 2(2n + 3) 4n + 4 4n + 10 Answer: B) 4n + 6 = 2(2n + 3)
Explanation: So the sum is always even but never a multiple of 4. SLO M-09-B-15 · Knowledge
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60. A conjecture is a statement that: is believed to be true but has not been proved is known to be false has been proved is accepted without proof Answer: A) is believed to be true but has not been proved
Explanation: A conjecture becomes a theorem once someone proves it. SLO M-09-B-14 · Knowledge
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61. The letters Q.E.D. at the end of a proof mean: which was to be demonstrated (the proof is complete) question ends directly quite easily done the next step follows Answer: A) which was to be demonstrated (the proof is complete)
Explanation: Q.E.D. — quod erat demonstrandum. SLO M-09-B-13 · Knowledge
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62. A single example that shows a general statement is false is called a: counterexample proof theorem lemma Answer: A) counterexample
Explanation: One counterexample is enough to disprove a general statement. SLO M-09-B-13 · Knowledge
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63. “The angles of a triangle add up to 180^circ” is: a conjecture a theorem an axiom a definition Answer: B) a theorem
Explanation: It is proved using the properties of parallel lines. SLO M-09-B-14 · Knowledge
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64. Prove that the sum of three consecutive integers is divisible by 3. Writing them as n, n + 1, n + 2, the sum is: 3(n + 1) 3n + 2 3n n + 3 Answer: A) 3(n + 1)
Explanation: n + (n + 1) + (n + 2) = 3n + 3 = 3(n + 1), a multiple of 3. SLO M-09-B-15 · Knowledge
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