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401.

If `A+B^T=[(1,3),(4,5)] and A^T-B=[(7,8),(-1,3)]` , then find matrices A and B.

Answer» Correct Answer - `A= [{:(4, 1), (6, 4):}]; B = [{:(-2, -2),(2, 1):}]`
402.

Find matrix X, if `[[3,5,-9],[-1,4,-7]]+X=[[6,2,3],[4,8,6]]`

Answer» `[{:(3,-3,12),(5,4,13):}]`
403.

If `({:((1)/(2), -(3)/(5)),((4)/(6), -(1)/(7)):}) = ({:(-a, b), (c, -d):})({:(1, 0), (0, 1):})` then find a, b,c and d.

Answer» Correct Answer - `a = -(1)/(2), b = -(3)/(5), c = (4)/(6) and d = (1)/(7)`
404.

If `5A=[{:(5,10,-15),(2,3," "4),(1,0,-5):}]`, find A.

Answer» `[{:(1,2,-3),((1)/(2),(3)/(5)," "(4)/(5)),((1)/(5),0,-1):}]`
405.

Find matrices A and B, if `2A-B=[{:(6,-6,0),(-4," "2,1):}]" and "2B+A=[{:(" "3,2," "5),(-2,1,-7):}].`

Answer» `A=[{:(3,-2," "1),(-2," "1,-1):}]" and "B=[{:(0,4," "4),(0,0,-6):}]`
406.

If `B = [{:(-1, 0), (2, 4):}] " and " f(x) = x^(2) - 4x + 5,` then find f(B).

Answer» Correct Answer - `[{:(10, 0), (-2, 5):}]`
407.

Find matrices A and B, if `A+B=[{:(1,0," "2),(5,4,-6),(7,3," "8):}]" and "A-B=[{:(-5,-4,8),(11," "2,0),(-1," "7,4):}].`

Answer» `A=[{:(-2,-2,5),(8,3,-3),(3,5,6):}]" and "B=[{:(3," "2,-3),(-3," "1,-3),(4,-2," "2):}]`
408.

Find matrices A and B, if A + B = \(\begin{bmatrix}1&0 & 2 \\[0.3em]5& 4 & -6\\[0.3em]7 & 3& 8\end{bmatrix}\) and A - B = \(\begin{bmatrix}-5&-4 & 8 \\[0.3em]11& 2 & 0\\[0.3em]-1 & 7& 4\end{bmatrix}.\) A + B = [(1,0,2)(5,4,-6)(7,3,8)]A - B = [(-5,-4,8)(11,2,0)(-1,7,4)].

Answer»

Add (A + B) and (A - B)

We get (A + B) + (A - B) = \(\begin{bmatrix}1& 0& 2 \\[0.3em]5 & 4 &-6 \\[0.3em]7 & 3 & 8\end{bmatrix}\) + \(\begin{bmatrix}-5& -4& 8 \\[0.3em]11 & 2 &0 \\[0.3em]-1 & 7 & 4\end{bmatrix}\)

2A = \(\begin{bmatrix}-4& -4& 10 \\[0.3em]16 & 6 &-6 \\[0.3em]6 & 10 & 12\end{bmatrix}\)

A = \(\begin{bmatrix}-2& -2& 5 \\[0.3em]8 & 3 &-3 \\[0.3em]3 & 5 & 6\end{bmatrix}\)

Now Subtract (A - B) from (A + B)

(A + B) - (A - B) = \(\begin{bmatrix}1& 0& 2 \\[0.3em]5 & 4 &-6\\[0.3em]7 & 3& 8\end{bmatrix}\) - \(\begin{bmatrix}-5& -4& 8 \\[0.3em]11 & 2 &0\\[0.3em]-1 & 7& 4\end{bmatrix}\) 

(2B) = \(\begin{bmatrix}6& 4& -6 \\[0.3em]-6 & 2 &-6\\[0.3em]8 & -4& 4\end{bmatrix}\)

B = \(\begin{bmatrix}3& 2& -3 \\[0.3em]-3 & 1 &-3\\[0.3em]4 & -2&2\end{bmatrix}\)

Conclusion: A = \(\begin{bmatrix}-2& -2&5 \\[0.3em]8 & 3 &-3\\[0.3em]3 & 5&6\end{bmatrix},\) B = \(\begin{bmatrix}3& 2&-3 \\[0.3em]-3 & 1 &-3\\[0.3em]4 & -2&2\end{bmatrix}\) 

409.

Compare the product , `({:(-5, 1),(6, -1), (-2, 0):}) ({:(4, -5, -1), (5, 6, 1):})((5), (-4), (1))`

Answer» Correct Answer - `[(-193), (232), (-78)]`
410.

If `A = [{:(2, -3), (4, 1):}], B = [{:(2, 3), (5, 0):}]" and " C = [{:(-1, 2),(0, 5):}]` then find A(B + C).

Answer» Correct Answer - `[{:(-13, -5), (9, 25):}]`
411.

If A and B are two matrices such that A + B = `[{:(3, 8),(11, 6):}] " and " A-B = `[{:(5, 2),(-3, -6):}]`, then find the matrices A and B.

Answer» Correct Answer - `A = [{:(4, 5), (4, 0):}]; B = [{:(-1, 3), (7, 6):}]`
412.

If `A xx [{:(-3, 4),(5, 10):}] = [{:(13, 6):}]`, then find A.

Answer» Correct Answer - `[-2 (7)/(5)]`
413.

Two friends Jack and Jill attend IIT entrance test which has three sections, Mathematics, Physics and Chemistry.Each question in Mathematics, Physics and Chemistry carry 5 marks, 8 marks and 3 marks respectively. Jack attempted 10 questions in Mathematics, 12 in Physics and 6 in Chemistry while Jill attemped 18, 5 and 9 questions in Mathematics, Physics and Chemistry respectively Assuming that all the questions attempted were correct, find the individual marks obtained by the boys by showing the above information as a matrix product.

Answer» Correct Answer - Marks obtained by Jack = 164
Marks obtained by Jill = 157
414.

If the rank of the matrix `[[-1,2,5],[2,-4,a-4],[1,-2,a+1]]` is `1` then the value of `a` is (A) `-1` (B) 2 (C) `-6` (D) 4A. `2, if a=-6`B. `2, if a=1`C. `1, if a=2`D. `1, if a=-6`

Answer» Correct Answer - B::D
Let `A= [[-1, 2, 5],[2, -4, a-4],[1, -2, a+1]]`
Applying `R_(2) rarr R_(2) 2 R_(1) and R_(3) rarr R_(3) + R_(1)`, then
`A = [[-1, 2, 5],[0,0,a+6],[0,0,a+6]]`
Applying `R_(3) rarr R_(3) - R_(2)`, then
`A = [[-1, 2, 5],[0,0,a+6],[0,0,0]]`
For `a = - 6 , p (A) = 1`
For `a = 1,2,p (A) = 2`
415.

If `A=[[3,-3,4],[2,-3,4],[0,-1,1]]` , thenA. `adj(adjA)=A`B. `abs(adj(adj(A)))=1`C. `abs(adj(A))=1`D. None of these

Answer» Correct Answer - A::B::C
Here, `abs(A) = abs((3, -3, 4),(2, -3, 4),(0, -1, 1))`
`= 3 (-3+4) + 3 (2-0) + 4 (-2+0)= 1 ne 0`
`because adj (adjA) = abs(A)^(3-2) A = A ` ...(i)
and `abs(adj (A) ) = abs(A)^(3-1) = abs(A)^(2) = 1^(2) = 1 `
Also, `abs(adj(adj(A))) = abs(A ) = 1 ` [ from Eq. (i) ]
416.

If matrix a satisfies the equation `A^(2)=A^(-1)`, then prove that `A^(2^(n))=A^(2^((n-1))), n in N`.

Answer» `A^(2^(n))=A^(2.2^(n-1))=(A^(2))^(2^(n-1))`
`=(A^(-1))^(2^(n-1))=(A^(2^(n-1)))^(-1)=(A^(2.2^(n-1)))^(-1)`
`=((A^(2))^(2^(n-1)))^(-1)=((A^(-1))^(-1))^(2^((n-2)))=A^(2^((n-2)))`
417.

Fiven the matrix `A= [[-1,3,5],[1,-3,-5],[-1,3,5]]` and X be the solution set of the equation `A^(x)=A,` where `x in N -{1}`. Evaluate `prod((x^(3)+1)/(x^(3)-1))` where the contincued extends for all `x in X`.

Answer» `A= [[-1,3,5],[1,-3,-5],[-1,3,5]][[-1,3,5],[1,-3,-5],[-1,3,5]]=[[-1,3,5],[1,-3,-5],[-1,3,5]]`
= A
`therefore A^(2) = A^(3) = A^(4) = A^(5) = …= A`
but given `A^(x) = A`
`rArr x = 2, ,3, 4, 5, … [because x ne 1,` given]
`therefore prod ((x^(3)+1)/(x^(3)-1)) = prod ((x+1)/(x-1)) prod (x^(2)-x+1)/(x^(2)+x+1))` On putting `x = 2, 3, 4, 5...`
`prod ((x^(3)+1)/(x^(3)-1)) =lim_(nrarr infty) prod_(x=2)^(n) ((x+1)/(x-1)) prod_(x=2)^(n) (x^(2)-x+1)/(x^(2)+x+1))`
`lim _(n rarr infty)((3cdot 4cdot 5...(n-1) n (n+1) )/(1cdot 2cdot 3 ... (n-3) (n-2)(n-1)))`
`xxlim _(n rarr infty)((3cdot7cdot... (n^(2)-m+1) )/(7cdot 13 ... (n^(2)-n+1) (n^(2) + n+1)))`
`=lim _(n rarr infty) (n(n+1))/(2)xx 3/(n^(2)+n+1)`
`= 3/2lim _(n rarr infty) ((1+1/n))/((1+1/n+1/n^(2)))= 3/2cdot ((1+0))/((1+0+0))=3/2`
418.

Let A and B be matrices of order n. Provce that if (I - AB) is invertible, (I - BA) is also invertible and `(I-BA)^(-1) = I + B (I- AB)^(-1)A, ` where I be the dientity matrix of order n.

Answer» Here, `I -BA = BIB^(-1)-BABB^(-1) = B(I-AB)B^(-1)` ...(i)
Hence, `abs(I-BA) = abs(B)abs(I-AB) abs(B^(-1)) = abs(B) abs(I-AB) 1/abs(B)`
`= abs(I-AB)`
If `abs(I-AB)ne 0, "then" abs(I-BA) ne 0`
i.e. if `(I -AB)` is invertible, then `(I - BA)` is also invertible.
Now, `(I-BA) [ I + B (I-AB)^(-1)A]`
`= (I- BA) + (I-BA) B (I-AB)^(-1)A ` [ using Eq. (i)]
`= (I- BA) +B (I-AB) B^(-1) B (I-AB)^(-1)A `
`=(I-BA)B(I-AB)(I-AB^(-1))A`
`= (I - BA) + BA= I`
Hence, `(I- BA)^(-1)=I + B(I-AB)^(-1) A.`
419.

Find the value of x and y that satisfy the equations `[(3,-2),(3,0),(2,4)] [(y,y),(x,x)]=[(3,3),(3y,3y),(10,10)]`

Answer» Given `[(3,-2),(3,0),(2,4)] [(y,y),(x,x)]=[(3,3),(3y,3y),(10,10)]`
or `[(3y-2x,3y-2x),(3y,3y),(2y+4x,2y+4x)]=[(3,3),(3y,3y),(10,10)]`
Comparing elements we have
`3y-2x=3`
`2y+4x+10`
Solving (1) and (2), we get `x=3//2, y=2`
420.

If `A=[{:(2,3,-1),(1,4,2):}]` and `B=[{:(2,3),(4,5),(2,1):}]` then AB and BA are defined and equal.

Answer» False,
Since AB is defined
`therefore AB=[{:(2,3,-1),(1,4,2):}][{:(2,3),(4,5),(2,1):}]=[{:(14,20),(22,25):}]`
Also, BA is defined
`therefore BA=[{:(2,3),(4,5),(2,1):}][{:(2,3,-1),(1,4,2):}]`
`=[{:(7,18,4),(13,32, 6),(5,10,0):}]`
`ABneBA`
421.

If A is skew-symmetric matrix then `A^(2)` is a symmetric matrix.

Answer» True
`because [A^(2)]=[A]^(2)`
`=[-A]^(2)`
`[because A=-A]`
`=A^(2)`
Hence, `A^(2)` is symmetric matrix
422.

If `A={:((a-a,b-b)):}" then "((1)/(ab))A=`A. `((1)/(b)+(1)/(b) (1)/(a)-(1)/(a))`B. `((1)/(a)-(1)/(a)(1)/(b)-(1)/(b))`C. `((1)/(b)-(1)/(b)(1)/(a)-(1)/(a))`D. `(a^(2)b" "-a^(2)b" "b^(2)a" "-b^(2)a)`

Answer» Correct Answer - C
Apply scalar product of a matrix.
423.

If `A={:[(0,-1),(1,0)]:}andB={:[(-1,0),(3,2)]:}`, then `AB^(2)` =A. `{:[(-3,-4),(-1,0)]:}`B. `{:[(-3,-4),(1,0)]:}`C. `{:[(-3,-4),(0,1)]:}`D. `{:[(-3,4),(1,0)]:}`

Answer» Correct Answer - B
(i) `AB^(2)=(AB)B`.
(ii) Find `B^(2)`, then find `AB^(2)`.
424.

If `A={:((3,1),(-4,5)):},B={:((-3,1),(4,-5)):}andC={:((2,1),(-1,3)):}`, thenA. AB=ACB. AC=BCC. BC=CBD. A(B+C)=AB+AC

Answer» Correct Answer - D
(i) Try from products AB, BC AC and verify from options.
425.

If `A={:[(1,7),(5,6)]:},B={:[(-3,2),(-1,5)]:}andC={:[(2,-3),(4,1)]:}`, then find A(B+C) and AB+AC.

Answer» Correct Answer - `{:[(20,41),(13,31)]:},{:[(-10,37),(-21,40)]:}{:[(20,41),(13,31)]:}`
426.

If the matrix `{:[(a,a+b),(a+b+c,a+b+c+d)]:}` is symmetric, then which of the following holds ?A. a=0B. b=0C. c=0D. d=0

Answer» Correct Answer - C
If A is symmetric matrix, then `A^(T)=A`.
427.

Let A and B be matrices of orders 3 × 2 and 2 × 4 respectively. Write the order of matrix AB.

Answer»

We are given that, 

Order of matrix A = 3 × 2 

Order of matrix B = 2 × 4 

We need to find the order of matrix AB. 

We know that, 

Matrix A × Matrix B = Matrix AB 

If order of matrix A is (m × n) and order of matrix B is (r × s), 

Then,

Matrices A and B can be multiplied if and only if n = r. 

That is, 

Number of columns in A = Number of rows in B 

Also, 

The order of resulting matrix AB comes out to be m × s. 

Applying it, 

Number of columns in A = 2 

Number of rows in B = 2 

This means, 

Matrices A and B can be multiplied, 

And its order will be given as : 

Order of matrix AB = 3 × 4 

Thus, 

Order of matrix AB = 3 × 4

428.

If `A={:[(4,-2),(3,-1),(2,5)]:}andB={:[(-7,2),(5,9),(3,4)]:}`, then 2A+7B=A. `{:[(41,10),(40,60),(26,38)]:}`B. `{:[(-41,10),(41,61),(26,38)]:}`C. `{:[(14,5),(30,-60),(24,26)]:}`D. `{:[(-41,10),(41,61),(25,38)]:}`

Answer» Correct Answer - D
First find the scalar product and add the two matrices.
429.

Which of the following is a `1xx3` matrix ?A. `[{:(1),(2),(3):}]`B. `[1,2,3,4]`C. [4,5,6]D. All the above.

Answer» Correct Answer - C
The matrix with one row and 3 columns has an order of `1xx3`
430.

If `A={:[(2,3),(4,1)]:},B={:[(9,5),(-6,1)]:}andC={:[(2,-6),(-3,1)]:}` then find (A+B)+C.

Answer» Correct Answer - `{:[(13,2),(-5,3)]:}`
431.

The product of `{:[(a,b),(c,d)]:}and{:[(x),(y)]:}` is _________ .

Answer» Correct Answer - `{:[(ax,by),(cx,dy)]:}`
432.

If `A={:[(p,0),(0,p)]:}" then "A^(n+1)` is _________ .A. `{:[(p,0),(0,p)]:}`B. `{:[(p^(n+1),0),(0,p^(n+1))]:}`C. `{:[(np,0),(0,np)]:}`D. None of these

Answer» Correct Answer - B
Given `A={:[(p,0),(0,P)]:}`
`A=P={:[(1,0),(0,1)]:}`
`A=PI`
`A^(n+1)=P^(n+1)xxI^(n+1)=P^(n+1)I(becauseI^(n)=I)`
`=P^(n+1){:[(1,0),(0,1)]:}={:[(p^(n+),0),(0,P^(n+1))]:}`.
433.

If the orders of matrices `A^(T),BandC^(T)" are "3xx4,2xx3and1xx2` respectively, then the order of the matrix `(AB^(T))C` isA. `3xx2`B. `2xx3`C. `4xx2`D. `4xx1`

Answer» Correct Answer - D
If A is `mxxn` matrix, B is `nxxp` matrix, then the order of AB is `mxxp`.
434.

The number of elements that a square matrix of order n has below its leading diagonal, isA. `(n(n+1))/2`B. `(n(n-1))/2`C. `((n-1)(n-1))/2`D. `((n+1)(n+1))/2`

Answer» Correct Answer - B
There `aren^2` elements in a square matrix of order n out of which n elements other than diagonal elemenets is `(n^2-n)`.
Half of these elements are above the diagonal and half are below the diagonal.
So, required number of elements is `(n^2-n)/2=1/2n(n-1)`.
435.

If a matrix has 7 elements, then the order of the matrix can beA. `4xx3`B. `3xx4`C. `4xx1`D. None of these

Answer» Correct Answer - D
Number of rows `xx` Number of columns=7
436.

The product of `{:[(2,-4,4)]:},and{:[(1),(3),(5)]:}` is ________ .

Answer» Correct Answer - [10]
437.

If `{:[(2,-1,0),(9,2,4),(6,3,-9)]:}`, find (k+l) A.

Answer» Correct Answer - `{:[(2k+2l,-k-l,0),(9k+9l,2k+2l,4k+4l),(6k+6l,3k+3l,-9k-9l)]:}`
438.

The product of `{:[(1),(2)]:}` and `{:[(3,4)]:}` is ________ .

Answer» Correct Answer - `{:[(3,4),(6,8)]:}`
439.

If `{:[(p),(q),(r)]:}andB={:[(3,4,5)]:}`, then AB isA. `{:[(3p,4p,5p),(3q,4q,5q),(3p,4q,5r)]:}`B. `{:[(3p,3q,3p),(4p,4q,4q),(5q,5p,5r)]:}`C. `{:[(3p,4p,5p),(3q,4q,5q),(3r,4r,5r)]:}`D. None of these

Answer» Correct Answer - C
Multiply the matrices A and B.
440.

If `A={:[(2,-3,1)]:}andB={:[(4),(2),(-2)]:}`, then find `2A^(T)+B`A. `{:[(4),(8),(5)]:}`B. `{:[(8),(-4),(0)]:}`C. `{:[(8),(4),(0)]:}`D. `{:[(8),(-8),(0)]:}`

Answer» Correct Answer - B
Find `A^(T)` and find the sum.
441.

If the matrix `A={:[(5,-3),(5,-3)]:}," then "A^(n+1)` = ________ .A. `{:[(5,-3),(5,-3)]:}`B. `{:[(5,3),(5,3)]:}`C. `2^(n){:[(5,-3),(5,-3)]:}`D. `2^(n+1){:[(5,-3),(5,-3)]:}`

Answer» Correct Answer - C
`A={:[(5,-3),(5,-3)]:}`
`A^(2)={:[(5,-3),(5,-3)]:}{:[(5,-3),(5,-3)]:}`
`{:[(25-15,-15+9),(25-15,-15+9)]:}`
`{:[(10,-6),(10,-6)]:}=2{:[(5,-3),(5,-3)]:}`
`A^(3)=A^(2)*A`
`{:[(10,-6),(10,-6)]:}{:[(5,-3),(5,-3)]:}`
`{:[(50-30,-30+18),(50-30,-30+18)]:}={:[(20,-12),(20,-12)]:}`
`=4{:[(5,-3),(5,-3)]:}=2^(2){:[(5,-3),(5,-3)]:}`
`A^(n+1)=2^(n){:[(5,-3),(5,-3)]:}`.
442.

If `A={:[(5,6),(7,8)]:}," then "(A+A^(T))/(2)` is _______ .A. symmetricB. skew symmetricC. diagonalD. unit matrix

Answer» Correct Answer - A
`A={:[(5,6),(7,8)]:},A^(T)={:[(5,7),(6,8)]:}`
`A+A^(T)={:[(5+5,6+7),(7+6,8+8)]:}`
`A+A^(T)={:[(10,13),(13,16)]:}`
`(1)/(2)(A+A^(T))={:[((10)/(2),(13)/(2)),((13)/(2),(16)/(2))]:}={:[(5,(13)/(2)),((13)/(2),8)]:}`
`(1)/(2)[(A+A^(T))]^(T)=(1)/(2)[A+A^(T)]`
`:." It is symmetric".`
443.

If all the diagonal elements in a diagonal matrix is 0, then it is a ________ matrix.

Answer» Correct Answer - null
444.

The number of column of the matrix `[{:(1,2,3),(4,5,6):}]` is ________A. 2B. 6C. 3D. 5

Answer» Correct Answer - C
Cound the number of vertical arrays of elements.
445.

`{:[(0,-3),(3,0)]:}` is a ________ matrix.

Answer» Correct Answer - skew-symmetric
446.

If A is any square matrix, then `(1)/(2) (A-A^(T))` is a ____matrix.

Answer» Correct Answer - skew-symmetric
447.

If `(A + B^(T))^(T)` is a matrix of order `4 xx 3`, then the order of matrix B is____.

Answer» Correct Answer - ` 4 xx 3`
448.

If A =\(\begin{vmatrix}α&2\\2&α\end{vmatrix}\)and |A3 | = 125, then α = ___________A = [(α, 2) (2, α)](a) ±3 (b) ±2 (c) ±5 (d) 0

Answer»

Correct option is : (a) ±3

|A3 | = 125 

|A|3 = 53 …….[∵ |An | = |A|n , n ∈ N] 

∴ |A| = 5 

\(\begin{vmatrix}α&2\\2&α\end{vmatrix}\)=5

α2 – 4 = 5 

α2 = 9 

∴ α = ± 3

449.

The number of all possible matrices of order 3 x 3 with each entry 0 or 1 is:(A) 27     (B) 18     (C) 81     (D) 512

Answer»

The correct answer is D.
The given matrix of the order 3 x 3 has 9 elements and each of these elements can be either 0 or 1. 

Now, each of the 9 elements can be filled in two possible ways. 

Therefore, by the multiplication principle, the required number of possible matrices is 29 = 512

450.

If `A=[{:(2,-1,3),(-4," "5,1):}]" and "B=[{:(2,3),(4,-2),(1,5):}]` then find AB and BA. Show that `ABneBA.`

Answer» Here, A is a `2xx3` matrix and B is a `3xx2` matrix.
So, number of columns in A =number of rows in B.
`:.` AB exists and it is a `2xx2` matrix.
`AB=[{:(2,-1,3),(-4," "5,1):}][{:(2,3),(4,-2),(1,5):}]`
`=[{:(2.2+(-1).4+3.1," "2.3+(-1).(-2)+3.5),(-4.2+5.4+1.1,-4.3+5.(-2)+1.5):}]`
`=[{:(4-4+3,6+2+15),(-8+20+1,-12-10+5):}]=[{:(3," "23),(13,-17):}].`
Again, B is a `3xx2` matrix and A is a `2xx3` matrix.
So, number of columns in B=number of rows in A.
`:.` BA exists and it is a `3xx3` matrix.
`BA=[{:(2,3),(4,-2),(1,5):}][{:(2,-1,3),(-4," "5,1):}]`
`=[{:(2.2+3.(-4),2.(-1)+3.5,2.3+3.1),(4.2+(-2).(-4),4.(-1)+(-2).5,4.3+(-2).1),(1.2+5.(-4),1.(-1)+5.5,1.3+5.1):}]`
`=[{:(4-12,-2+15,6+3),(8+8,-4-10,12-2),(2-20,-1+25,3+5):}]=[{:(-8,13,9),(16,-14,10),(-18,24,8):}].`
Clearly, `ABneBA.`