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Published on: 02/02/2021
12th Standard Maths English Medium Discrete Mathematics Reduced Syllabus Important Questions With Answer Key 2021
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.
Show that p v (q ∧ r) is a contingency.
2.
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
3.
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 AΛB
4.
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 AVB
5.
Write the converse, inverse, and contrapositive of each of the following implication.
If x and y are numbers such that x = y, then x2 = y2
6.
Fill in the following table so that the binary operation ∗ on A = {a, b, c} is commutative.
| * | a | b | c |
| a | b | ||
| b | c | b | a |
| c | a | c |
7.
Let p: Jupiter is a planet and q: India is an island be any two simple statements. Give verbal sentence describing each of the following statements.
(i) ¬p
(ii) p ∧ ¬q
(iii) ¬p ∨ q
(iv) p➝ ¬q
(v) p↔q
8.
How many rows are needed for following statement formulae?
(( p ∧ q) ∨ (¬r ∨¬s)) ∧ (¬ t ∧ v))
9.
How many rows are needed for following statement formulae?
\(p \vee \neg t \wedge(p \vee \neg s)\)
10.
Write the statements in words corresponding to ¬p, p ∧ q , p ∨ q and q ∨ ¬p, where p is ‘It is cold’ and q is ‘It is raining'.
11.
Verify (p ∧ ~p) ∧ (~q ∧ p) is a tautlogy, contradiction or contingency.
12.
Let A be Q\{1}. Define ∗ on A by x*y = x + y − xy. Is ∗ binary on A? If so, examine the commutative and associative properties satisfied by ∗ on A.
13.
Verify
(i) closure property
(ii) commutative property
(iii) associative property
(iv) existence of identity and
(v) existence of inverse for the operation ×11 on a subset A = {1, 3, 4, 5, 9} of the set of remainders {0,1, 2, 3, 4, 5, 6, 7, 8, 9,10}
14.
Verify
(i) closure property
(ii) commutative property
(iii) associative property
(iv) existence of identity and
(v) existence of inverse for the operation +5 on Z5 using table corresponding to addition modulo 5.
15.
Verify
(i) closure property
(ii) commutative property
(iii) associative property
(iv) existence of identity, and
(v) existence of inverse for following operation on the given set m*n = m + n - mn; m, n ∈Z
16.
Construct the truth table for (-p) v (q ∧ r)
17.
In (z, *) where * is defined by a * b = ab, prove that * is not a binary operation on z.
18.
Construct the truth table for the following statements.
( p V q) V ¬q
19.
20.
In (S, *), is defined by x * y = x where x, y \(\in \) S, then
associative
Commutative
associative and commutative
neither associative nor commutative
21.
In (N, *), x * y = max(x, y), x, y \(\in \) N then 7 * (-7)
7
-7
0
-49
22.
'-' is a binary operation on ___________
~
Q-{0}
R-{0}
Z
23.
'+' is not a binary operation on ___________
~
z
c
Q- {0}
24.
If p is true and q is unknown, then _________
~ p is true
p v (~p) is false
p ∧ (~p) is true
p v q is true
25.
Define * on Z by a * b = a + b + 1 ∀ a,b \(\in \) Z. Then the identity element of z is ________
1
0
1
-1
26.
The identity element in the group {R - {1},x} where a * b = a + b - ab is __________
0
1
\(\frac { 1 }{ a-1 } \)
\(\frac { a }{ a-1 } \)
27.
Which of the following is a contradiction?
p v q
p ∧ q
q v ~ q
q ∧ ~ q
28.
If * is defined by a * b = a2 + b2 + ab + 1, then (2 * 3) * 2 is _____________
20
40
400
445
29.
The proposition p ∧ (¬p ∨ q) is
a tautology
a contradiction
logically equivalent to p ∧ q
logically equivalent to p ∨ q
30.
In the last column of the truth table for ¬( p ∨ ¬q) the number of final outcomes of the truth value 'F' are
1
2
3
4
31.
Which one of the following statements has the truth value T?
sin x is an even function
Every square matrix is non-singular
The product of complex number and its conjugate is purely imaginary
\(\sqrt 5\) is an irrational number
32.
In the set Q define a⊙b = a+b+ab. For what value of y, 3⊙(y⊙5) = 7?
y = \(\frac{2}{3}\)
y = \(\frac{-2}{3}\)
y = \(\frac{-3}{2}\)
y = 4
33.
The operation * defined by \(a * b =\frac{ab}{7}\) is not a binary operation on
Q+
Z
R
C
1.
| 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
2.
Given \(A=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) ,B=\left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) and\quad C=\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 0 & 0 \\ 0 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 0 \\ 0 & 0 \\ 0 & 1 \end{matrix} \right) \vee \left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)
\((A\wedge B)\vee C=\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)
3.
Given \(A=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) ,B=\left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) and\quad C=\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) \vee \left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 1\wedge 0 & 0\wedge 1 \\ 0\wedge 1 & 1\wedge 0 \\ 1\wedge 1 & 0\wedge 0 \end{matrix}\begin{matrix} 1\wedge 0 & 0\wedge 1 \\ 0\wedge 1 & 1\wedge 0 \\ 0\wedge 0 & 1\wedge 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 0 & 0 \\ 0 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 0 \\ 0 & 0 \\ 0 & 1 \end{matrix} \right) \) [∵ a៱b=max(a,b)]
4.
Given \(A=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) ,B=\left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) and\quad C=\left( \begin{matrix} 1 & 1 \\ 0 & 1 \\ 1 & 1 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 1 & 0 \\ 0 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 0 \\ 0 & 1 \\ 0 & 1 \end{matrix} \right) \vee \left( \begin{matrix} 0 & 1 \\ 1 & 0 \\ 1 & 0 \end{matrix}\begin{matrix} 0 & 1 \\ 1 & 0 \\ 0 & 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 1\vee 0 & 0\vee 1 \\ 0\vee 1 & 1\vee 0 \\ 1\vee 1 & 0\vee 0 \end{matrix}\begin{matrix} 1\vee 0 & 0\vee 1 \\ 0\vee 1 & 1\vee 0 \\ 0\vee 0 & 1\vee 1 \end{matrix} \right) \)
\(=\left( \begin{matrix} 1 & 1 \\ 1 & 1 \\ 1 & 0 \end{matrix}\begin{matrix} 1 & 1 \\ 1 & 1 \\ 0 & 1 \end{matrix} \right) \) [∵ a∨b=max(a,b)]
5.
If x and y are numbers such that x = y, then x2 = y2
Converse statement :
If x and y are numbers such that x2 = y2 then x = y
Inverse statement :
If x and y are numbers such that x ≠ y then x2 ≠ y2
Contrapositive statement :
If x and y are numbers such that x2≠ y2 then x ≠ y
6.
Given * on A is commutative
Given b * a = c ⇒ a * b = c
Given c * a = a ⇒ a * c = a
Given b * c = a ⇒ c * b = a
Hence
| * | a | b | c |
| a | b | c | a |
| b | c | b | a |
| c | a | a | c |
7.
Given p : Jupiter is a planet and
q : India is an island.
(i) ¬p : Jupiter is not a planet.
(ii) p ∧ ¬q : Jupiter is a planet and India is not an island.
(iii) ¬p ∨ q : Jupiter is not a planet or India is an island.
(iv) p➝ ¬q : If Jupiter is a planet then India is not an island.
(v) p↔q : Jupiter is a planet if and only if India is an island.
8.
(( p ∧ q) ∨ (¬r ∨¬s)) ∧ (¬ t ∧ v)) contains 6 variables p, q, r, s, t, and v. Hence the corresponding truth table will contain 26 = 64 rows.
9.
p ∨ ¬ t ( p ∨ ¬s) contains 3 variables p, s, and t. Hence the corresponding truth table will contain 23 = 8 rows
10.
(1) ¬p: It is not cold.
(2) p ∧ q: It is cold and raining.
(3) p ∨ q: It is cold or raining.
(4) q ∨ ¬p: It is raining or it is not cold
Observe that the statement formula ¬ p has only 1 variable p and its truth table has 2 = ( 21 ) rows. Each of the statement formulae p ∧ q and p ∨ q has two variables p and q. The truth table corresponding to each of them has 4 = (22 ) rows. In general, it follows that if a statement formula involves n variables, then its truth table will contain 2n rows.
11.
| p | q | ~p | p∧~p) | ~q | (~q)∧p | (p∧~p) ∧ (~q∧p) |
| T | T | F | F | F | F | F |
| T | F | F | F | T | T | F |
| F | T | T | F | F | F | F |
| F | F | T | F | T | F | F |
Since the entries in the last column are F, (p ∧ ~p) ∧ (~q ∧ P) is a contradiction
12.
given A = {Q\{1}}
A is defined on A by x*y = x+y-xy
Let x,y ≠ 1
∴ x*y = x + y - xy
Now to prove that x + y - xy ≠ 1
Let us assume that x + y - xy = 1
x+y-xy-1 = 0
(x-1)-y(x-1) = 0
(x-1)(1-y) = 0
x =1 or y = 1 which is a false [∵x, y ≠ 1]
∴ is a binary operation on A.
Commutative property:
Let x,y ∈A ⇒ x, y≠1
∴x*y = x+y-xy
and y*x = y+x-yx
⇒x+y = y*x∀x, y∈A
A has commutative property under *
Associative property:
Let x,y,z ∊A ⇒x,y,z≠1
Consider (x*y)*z = (x+y-xy)*z
= x +y~xy +z- (x +y-xy)z
= x +y-xy+ z-xz- yz + xyz
= x +y+z-xy-yz-zx +xyz ...(1)
= x +y+z - yz - x (y + z - yz)
= x +y +z-yz-zy-xz +xyz ..(2)
From (1) & (2), (x*y)*z = x*(y*z)
A has associative property under *.
13.
The table for the operation x11 is as follows.
| x11 | 1 | 3 | 4 | 5 | 9 |
| 1 | 1 | 3 | 4 | 5 | 9 |
| 3 | 3 | 9 | 1 | 4 | 5 |
| 4 | 4 | 1 | 5 | 9 | 3 |
| 5 | 5 | 4 | 9 | 3 | 1 |
| 9 | 9 | 5 | 3 | 1 | 4 |
Following the same kind of procedure as explained in the previous example, a brief outline of the process of verification of the properties of ×11 on A is given below.
(i) Since each box has an unique element of A, ×11 is a binary operation on A.
(ii) The entries are symmetrical about the main diagonal. Hence ×11 has commutative property.
(iii) As usual, the associative property can be seen to be true.
(iv) The entries of both the row and column headed by the element 1 are identical. Hence 1 is the identity element.
(v) Since the identity 1 exists in each row and each column, the existence of inverse property is assured for ×11. The inverse of 1 is 1, that of 3 is 4, that of 4 is 3, 5 is 9, and, that of 9 is 5.
14.
It is known that Z5 = {[0], [1], [2], [3], [4]}. The table corresponding to addition modulo 5 is as follows: We take reminders {0,1,2,3,4} to represent the classes {[0], [1], [2], [3], [4]}.
| +5 | 0 | 1 | 2 | 3 | 4 |
| 0 | 0 | 1 | 2 | 3 | 4 |
| 1 | 1 | 2 | 3 | 4 | 0 |
| 2 | 2 | 3 | 4 | 0 | 1 |
| 3 | 3 | 4 | 0 | 1 | 2 |
| 4 | 4 | 0 | 1 | 2 | 3 |
(i) Since each box in the table is filled by exactly one element of Z5, the output a +5 b is unique and hence +5 is a binary operation.
(ii) The entries are symmetrically placed with respect to the main diagonal. So +5 has commutative property
(iii) The table cannot be used directly for the verification of the associative property. So it is to be verified as usual
For instance, (2+53)+5 4 = 0+5 4 = 4(mod 5)
and 2+5(3+54) = 2 +5 2 = 4(mod5)
Hence (2+53)+54 = 2+5(3+54)
Proceeding like this one can verify this for all possible triples and ultimately it can be shown that +5 is associative
(iv) The row headed by 0 and the column headed by 0 are identical. Hence the identity element is 0.
(v) The existence of inverse is guaranteed provided the identity 0 exists in each row and each column. From Table, it is clear that this property is true in this case. The method of finding the inverse of any one of the elements of Z5, say 2 is outlined below.
First find the position of the identity element 0 in the III row headed by 2. Move horizontally along the III row and after reaching 0, move vertically above 0 in the IV column, because 0 is in the III row and IV column. The element reached at the topmost position of IV column is 3. This element 3 is nothing but the inverse of 2, because, 2+5 5+ = 0 (mod5). In this way, the inverse of each and every element of Z5 can be obtained. Note that the inverse of 0 is 0, that of 1 is 4, that of 2 is 3, that of 3 is 2, and, that of 4 is 1.
15.
(i) The output m+ n - mn is clearly an integer and hence∗ is a binary operation on Z.
(ii) m*n = m+ n − mn = n + m − nm = n*m, ∀m,n∈Z. So ∗ has commutative property.
(iii) Consider (m*n)*p = (m+ n −m n)* p= (m+ n −mn) + p − (m+ n −m n) p
= m+ n + p −mn −m p − n p + m n p ... (1)
Similarly m*(n*p) = m*(n + p − n p) = m+ (n + p − n p) −m (n + p − n p)
= m+ n + p − n p −m n −mp + m n p ... (2)
From (1) and (2), we see that m*(n*p) = (m*n)*p. Hence * has associative property.
(iv) An integer e is to be found such that
m*e = e*m = m, ∀m∈Z ⇒ m + e - m e = m
⇒e(1-m) = 0 ⇒ e = 0 or m = 1. But m is an arbitrary integer and hence need not be equal to 1. So the only possibility is e = 0. Also m*0 = 0*m = m, ∀m∈Z. Hence 0 is the identity element and hence the existence of identity is assured.
(v) An element m'∈ Z is to be found such that m*m' = m' * m = e = 0, ∀m∈Z.
m*m' = 0 ⇒ m+m'-m m'= 0⇒ m m' = 0 ⇒ \(\frac{m}{m-1}\). when m = 1, m' is not defined.
When m = 2, m' is an integer. But except m = 2, m′ need not be an integer for all values of m. Hence inverse does not exist in Z.
16.
| p | q | r | ~p | q ∧ r | (~p) v (q ∧ r) |
| T | T | T | F | T | T |
| T | F | F | F | F | F |
| T | F | T | F | F | F |
| T | F | F | F | F | F |
| F | T | T | T | T | T |
| F | T | F | T | F | T |
| F | F | T | T | F | T |
| F | F | F | T | F | T |
17.
Let a = 2, b = -5
∴ a * b = ab
⇒ 2 * -5 = 2-5 = \(\frac{1}{2^5}\) ∉ z
* is not a binary operation on z.
18.
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 |
19.
(a)
20.
(a)
associative
21.
(a)
7
22.
(d)
Z
23.
(d)
Q- {0}
24.
(d)
p v q is true
25.
(d)
-1
26.
(a)
0
27.
(d)
q ∧ ~ q
28.
(d)
445
29.
(c)
logically equivalent to p ∧ q
30.
(c)
3
31.
(d)
\(\sqrt 5\) is an irrational number
32.
(b)
y = \(\frac{-2}{3}\)
33.
(b)
Z
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