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11th And 12th > Mathematics

MATRICES MCQs

Total Questions : 69 | Page 1 of 7 pages
Question 1.


If A=[abba] and A2=[αββα], then


  1.     α=a2+b2,β=ab
  2.     α=a2+b2,β=2ab
  3.     α=a2+b2,β=a2b2
  4.     α=2ab,β=a2+b2
 Discuss Question
Answer: Option B. -> α=a2+b2,β=2ab
:
B
A2=[αββα]=[abba][abba];α=α2+b2;β=2ab
Question 2.


If A=1tanθ2tanθ21 and AB = I, then B =


  1.     cos2θ2.A
  2.     cos2θ2.AT
  3.     cos2θ2.I
  4.     None of these
 Discuss Question
Answer: Option B. -> cos2θ2.AT
:
B
|A|=1+tan2θ2=sec2θ2AB=IBIA1[1001]1tanθ2tanθ21sec2θ2=cos2θ2.AT.
Question 3.


Let,
A=461302125, B=240112
and C=[123]
The expression which is not defined is: 


  1.     BB
  2.     CAB
  3.     A+B
  4.     A2+A
 Discuss Question
Answer: Option C. -> A+B
:
C
We can see from the options that if we take transpose of B,
B will be of 2 x 3 matrix which cannot be added to a 3 x 3 matrix, as for the addition the order should be the same.
Question 4.


If A=a000b000c, then An=


  1.     na000nb000nc
  2.     a000b000c
  3.     an000bn000cn
  4.     None of these
 Discuss Question
Answer: Option C. -> an000bn000cn
:
C
Since A2=A.A=a000b000ca000b000c=a2000b2000c2
And A3=a3000b3000c3,....An=An1.A=an1000bn1000cn1a000b000c=an000bn000cn.
Note: Students should remember this question as a formula.
Question 5.


If A is 3×4 matrix and B is a matrix such that A'B and BA' are both defined. Then B is of the type


  1.     3×4
  2.     3×3
  3.     4×4
  4.     4×3
 Discuss Question
Answer: Option A. -> 3×4
:
A
A3×4A4×3Now A'B defined
Bis 3×p
Again B3×pA4×3 defined p=4
B is 3×4.
Question 6.


For each real number x such that 1<x<1,let A(x) be the matrix (1x)1[1xx1] and z=x+y1+xyThen,


  1.     A(z)=A(x)+A(y)
  2.     A(z)=A(x)+[A(y)]1
  3.     A(z)=A(x)A(y)
  4.     A(z)=A(x)A(y)
 Discuss Question
Answer: Option C. -> A(z)=A(x)A(y)
:
C
A(z)=A(x+y1+xy)=[1+xy(1x)(1y)] 1(x+y1+xy)(x+y1+xy)1
A(x).A(y)=A(z)
Question 7.


If A=[cosθsinθsinθcosθ],B=[1011],C=ABAT,then ATCnA equals to(nϵZ+)


  1.     [n110]
  2.     [1n01]
  3.     [011n]
  4.     [10n1]
 Discuss Question
Answer: Option D. -> [10n1]
:
D
A=[cosθsinθsinθcosθ]AAT=I          (i)Now,C=ABATATC=BAT       (ii)Now ATCnA=ATC.Cn1A=BATCn1A(from(ii))=BATC.Cn2A=B2ATCn2A=.......=Bn1ATCA=Bn1BATA=Bn=[10n1]
Question 8.


If A and B are two non singular matrices and both are symmetric and commute each other then


  1.     Both A1B and A1B1 are symmetric
  2.     A1B is symmetric but A1B1 is not symmetric
  3.     A1B1  is symmetric but A1B is not symmetric
  4.     Neither A1B nor A1B1 are symmetric
 Discuss Question
Answer: Option A. -> Both A1B and A1B1 are symmetric
:
A
AB =BA
Previous & past multiplying both sides by A1.
A1(AB)A1=A1(BA)A1(A1A)(BA1)=A1B(AA1)(BA1)1=(A1B)1=(A1)1B1(reversal laws)=A1B(as B=B1)(A1)1=A1A1B is symmetric
Similarly for A1B1.
Question 9.


A=[aij]n×n and aij=i2j2 then A is necessarily


  1.     a unit matrix
  2.     symmetric matrix
  3.     skew symmetric matrix
  4.     zero matrix
 Discuss Question
Answer: Option C. -> skew symmetric matrix
:
C
aji=j2i2=(i2j2)=aij 
Question 10.


If A is a non-diagonal involutory matrix, then


  1.     A - I = 0
  2.     A + I = 0
  3.     A - I is non zero singular
  4.     none of these
 Discuss Question
Answer: Option C. -> A - I is non zero singular
:
C
A2=IA2I=0
(A+I)(A-I)=0
either |A+I|=0 or
|AI|=0
If |AI|0, then (A+I)(AI)=0A+I=0 which is not so
|AI| and  AI0.

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