Question Details

Let = 1 0 0 1 and  P = 2 0 0 3 . Let  Q = x y z 4 for some non-zero real numbers x , y and  z  for which there

is a  2 × 2  matrix  R  with all entries being non-zero real numbers, such that  Q R = R P . Then which of the

following statements is (are) TRUE?


Options

A

The determinant of Q - 2I is zero

B

The determinant of Q - 6I is 12

C

The determinant of Q - 3I is 15

D

yz = 2

Show Answer

Correct Answer :

Option A

The determinant of Q - 2I is zero

Option B

The determinant of Q - 6I is 12

Solution :

The correct statements are:
1. The determinant of Q - 2I is zero
2. The determinant of Q - 6I is 12

Step-by-step Explanation:

Let the given matrices be:
I = 1 0 0 1 ,
P = 2 0 0 3 ,
Q = x y z 4

where x,y,z are non-zero real numbers. We are given that there exists a 2×2 matrix R with all non-zero real entries such that:

Q R = R P

Let R = a b c d where a,b,c,d0.

Substituting Q, R, and P into the equation QR=RP yields:
x y z 4 a b c d = a b c d 2 0 0 3

By matrix multiplication, we obtain:
xa+yc xb+yd za+4c zb+4d = 2a 3b 2c 3d

Comparing corresponding elements, we get the following system of equations:
(1) xa+yc=2a
(2) xb+yd=3b
(3) za+4c=2cza=-2c
(4) zb+4d=3dzb=-d

From equations (3) and (4), since a,b0:
z = - 2 c a = - d b
This gives:
c a = d 2 b

Let ca=k. Then c=ka and d=2kb.
Consequently, we can write z as:
z = - 2 k

Now, let's substitute these expressions into equations (1) and (2):
From (1):
( x - 2 ) a + y ( k a ) = 0 x - 2 + y k = 0 x - 2 = - y k
From (2):
( x - 3 ) b + y ( 2 k b ) = 0 x - 3 + 2 y k = 0 x - 3 = - 2 y k

Let yk=m. The system becomes:
x - 2 = - m
x - 3 = - 2 m

Solving for m by subtracting the second equation from the first:
1 = m
Thus, yk=1.
Substituting m=1 back, we find:
x = 2 - 1 = 1

Now, let's determine the value of yz:
y z = y ( - 2 k ) = - 2 ( y k ) = - 2 ( 1 ) = - 2

Hence, the matrix Q is:
Q = 1 y z 4 with yz=-2.

Checking Statement 1:
We evaluate Q-2I:
Q - 2 I = 1-2 y z 4-2 = -1 y z 2
The determinant is:
det ( Q - 2 I ) = ( - 1 ) ( 2 ) - y z = - 2 - ( - 2 ) = 0
Thus, Statement 1 is TRUE.

Checking Statement 2:
We evaluate Q-6I:
Q - 6 I = 1-6 y z 4-6 = -5 y z -2
The determinant is:
det ( Q - 6 I ) = ( - 5 ) ( - 2 ) - y z = 10 - ( - 2 ) = 12
Thus, Statement 2 is TRUE.

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