12th Standard Syllabus & Materials
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TN 12th Computer Applications வலையமைப்பு வடமிடல் Sample Question Papers Study Material - QB365 Set A

Published on: 22/01/2020
Discrete Mathematics
Download Tamil Nadu 12th Standard Maths question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.
Questions + Answers key
Take MCQ Maths Test1.
Let G = {1, w, w2) where w is a complex cube root of unity. Then find the universe of w2. Under usual multiplication.
2.
Let S be the set of positive rational numbers and is defined by a * b = \(\frac{ab}{2}\). Then find the identity element and the inverse of 2.
3.
In the set of integers under the operation * defined by a * b = a + b - 1. Find the identity element.
4.
Show that p v (q ∧ r) is a contingency.
5.
Show that p v (~p) is a tautology.
6.
Let \(A=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) ,B=\left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) ,C=\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)be any three boolean matrices of the same type.
Find (A∨B)∧C
7.
Determine the truth value of each of the following statements
(i) If 6 + 2 = 5 , then the milk is white.
(ii) China is in Europe or \(\sqrt3\) is an integer
(iii) It is not true that 5 + 5 = 9 or Earth is a planet
(iv) 11 is a prime number and all the sides of a rectangle are equal
8.
Let A = {a +\(\sqrt5\) b : a,b∈Z}. Check whether the usual multiplication is a binary operation on A.
9.
Determine whether ∗ is a binary operation on the sets given below.
(a*b) = a√b is binary on R
10.
How many rows are needed for following statement formulae?
\(p \vee \neg t \wedge(p \vee \neg s)\)
11.
Examine the binary operation (closure property) of the following operations on the respective sets (if it is not, make it binary)
\(a*b=\left( \frac { a-1 }{ b-1 } \right) ,\forall a,b\in Q\)
12.
Examine the binary operation (closure property) of the following operations on the respective sets (if it is not, make it binary)
a*b = a + 3ab − 5b2; ∀a,b∈Z
13.
Construct the truth table for the following statements.
( p V q) V ¬q
14.
Construct the truth table for the following statements.
¬(p ∧ ¬q)
15.
Construct the truth table for the following statements.
¬p ∧ ¬q
1.
Clearly 1 is the identity element of G
w2 . a-1 = e ⇒ w2 . a-1 = a-1 = w
Since w2 . w = w3 = 1
Inverse of w2 is w.
2.
Let a \(\in \) S and e be the identity element.
Then a * e = a ⇒ \(\frac { ae }{ 2 } \) = a
⇒ ae = 2a ⇒ e = 2
Let a-1 be the inverse of \(\frac { 1 }{ 2 } \)
Then \(\frac { 1 }{ 2 } \) * a-1 = e = \(\frac { 1 }{ 2 } \) * a-1 = e
⇒ \(\frac { { a }^{ -1 } }{ 2 } \frac { { a }^{ -1 } }{ 2 } \) = 2 ⇒ a-1 = 8.
3.
Let a be any element and e be the identity element.
The a * e = e * a = a
a * e = a ⇒ a + e -1 = a ⇒ e-1 = 0 ⇒ e = 1
∴ The identity element is 1
4.
| p | r | q | q ∧ r | p v (q ∧ r) |
| T | T | T | T | T |
| T | F | F | F | T |
| T | T | F | F | T |
| T | F | F | F | T |
| F | T | T | T | T |
| F | F | T | F | F |
| F | T | F | F | F |
| F | F | F | F | F |
∴p v (q Λ r) is a contingency
5.
| p | ~p | p v (~q) |
| T | F | T |
| F | T | T |
The last column contains only T
The given statement is a tautology
6.
Given \(A=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) ,B=\left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) and\quad C=\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)
\(\left( \begin{matrix} 1 & 1 \\ 1 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 1 \\ 1 & 1 \\ 0 & 1 \end{matrix} \right) \wedge \left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) =\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) \)
7.
(i) If 6 + 2 = 5, then the milk is white.
Let p: 6 + 2 = 5 (F)
q: Milk is white (T)
p ➝ q is having the truth value T
(ii) China is in Europe or \(\sqrt3\) is an integer.
p: China is in Europe (F)
q: \(\sqrt3\) is an integer (F)
p v q is having the truth value (F).
(iii) It is not true time 5 + 5 = 9 or Earth is a planet.
Let P: 5 + 5 = 9 is not true (T)
q: Earth is a planet (T
~p ∨ q is having the truth value T
(iv) 11 is a prime number and all the sides of a rectangle are equal.
p:11 is a prime number (T)
q: Allthe sides of arectangle areequal (F)
p ^ q is having the truth value F
8.
A = {a+\(\sqrt5\) b:a,b ∈ z}
Let C = a+\(\sqrt5\) b
B = c+\(\sqrt5\)d∈A
where a, b, c, d ∈ Z
[∵ ac + 5bd∈Z and ad+bc ∈Z]
∴ B = (a+\(\sqrt5\)b).(c+\(\sqrt5\)d)
= ac+\(\sqrt5\)ad+cb\(\sqrt5\) + 5bd
= (ac+5bd)+\(\sqrt5\)(ad+bc)∈A
∴ C.B ∈A∀ a, b, c, d∈Z
∴ Usual multiplicaition is a binary operation on.
9.
√b is not defined for negative values, b which also ∈ R.
Hence, a√b is not defined for all a, b ∈R
* is not a binary operation on R
10.
p ∨ ¬ t ( p ∨ ¬s) contains 3 variables p, s, and t. Hence the corresponding truth table will contain 23 = 8 rows
11.
In this problem a ∗ b is in the quotient form. Since the division by 0 is undefined, the denominator b -1 must be nonzero.
It is clear that b −1 = 0 if b = 1. As 1∈Q, ∗ is not a binary operation on the whole of Q. However it can be found that by omitting 1 from Q, the output a ∗b exists in Q\{1}. Hence ∗ is a binary operation on Q\{1}.
12.
Since × is binary operation on Z, a,b ∈ Z⇒ a × b = ab∈Z and b × b = b2∈Z ...(1)
The fact that + is binary operation on Z and (1) ⇒ 3ab = (ab + ab + ab) ∈Z and 5b2= (b2+b2+b2+b2+b2)∈Z ...(2)
Also a∈Z and 3ab ∈Z implies a+3ab∈Z ...(3)
(2),(3), the closure property of -on Z yield a * b = (a+3ab-5b2)∈Z. Since a * b belongs to Z, * is a binary operation on Z.
13.
Truth Table for ( p V q) ∧ ~q
| p | q | p V q | ~q | ( p V q) ∧ ~q |
| T | T | T | F | T |
| T | F | T | T | T |
| F | T | T | F | T |
| F | F | F | T | T |
14.
Truth Table for ~(p ∧ ~q)
| p | q | ~q | p ∧ ~q | ~(p ∧ ~q) |
| T | T | F | F | T |
| T | F | T | T | F |
| F | T | T | F | T |
| F | F | T | F | T |
15.
Truth Table for ~p ∧ ~q
| p | q | ~p | ~q | ~p ∧ ~q |
| T | T | F | F | F |
| T | F | F | T | F |
| T | F | F | T | F |
| F | T | T | F | F |
| F | F | T | T | T |
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