This set of Discrete Mathematics Assessment Questions and Answers focuses on “Types of Proofs”.

1. Let the statement be “If n is not an odd integer then square of n is not odd.”, then if P(n) is “n is an not an odd integer” and Q(n) is “(square of n) is not odd.” For direct proof we should prove _________

a) ∀nP ((n) → Q(n))

b) ∃ nP ((n) → Q(n))

c) ∀n~(P ((n)) → Q(n))

d) ∀nP ((n) → ~(Q(n)))

View Answer

Explanation: Definition of direct proof.

2. Which of the following can only be used in disproving the statements?

a) Direct proof

b) Contrapositive proofs

c) Counter Example

d) Mathematical Induction

View Answer

Explanation: Counter examples cannot be used to prove results.

3. Let the statement be “If n is not an odd integer then sum of n with some not odd number will not be odd.”, then if P(n) is “n is an not an odd integer” and Q(n) is “sum of n with some not odd number will not be odd.” A proof by contraposition will be ________

a) ∀nP ((n) → Q(n))

b) ∃ nP ((n) → Q(n))

c) ∀n~(P ((n)) → Q(n))

d) ∀n(~Q ((n)) → ~(P(n)))

View Answer

Explanation: Definition of proof by contraposition.

4. When to proof P→Q true, we proof P false, that type of proof is known as ___________

a) Direct proof

b) Contrapositive proofs

c) Vacuous proof

d) Mathematical Induction

View Answer

Explanation: Definition of vacuous proof.

5. In proving √5 as irrational, we begin with assumption √5 is rational in which type of proof?

a) Direct proof

b) Proof by Contradiction

c) Vacuous proof

d) Mathematical Induction

View Answer

Explanation: Definition of proof by contradiction.

6. A proof covering all the possible cases, such type of proofs are known as ___________

a) Direct proof

b) Proof by Contradiction

c) Vacuous proof

d) Exhaustive proof

View Answer

Explanation: Definition of exhaustive proof.

7. Which of the arguments is not valid in proving sum of two odd number is not odd.

a) 3 + 3 = 6, hence true for all

b) 2n +1 + 2m +1 = 2(n+m+1) hence true for all

c) All of the mentioned

d) None of the mentioned

View Answer

Explanation: Some examples are not valid in proving results.

8. A proof broken into distinct cases, where these cases cover all prospects, such proofs are known as ___________

a) Direct proof

b) Contrapositive proofs

c) Vacuous proof

d) Proof by cases

View Answer

Explanation: Definition of proof by cases.

9. A proof that p → q is true based on the fact that q is true, such proofs are known as ___________

a) Direct proof

b) Contrapositive proofs

c) Trivial proof

d) Proof by cases

View Answer

Explanation: Definition of trivial proof.

10. A theorem used to prove other theorems is known as _______________

a) Lemma

b) Corollary

c) Conjecture

d) None of the mentioned

View Answer

Explanation: Definition of lemma.

**Sanfoundry Global Education & Learning Series – Discrete Mathematics.**

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