Advertisements
Advertisements
Question
If `A=[[1,2,2],[2,1,2],[2,2,1]]` ,then show that `A^2-4A-5I=0` and hence find A-1.
Advertisements
Solution
`A=[[1,2,2],[2,1,2],[2,2,1]]`
`A^2=[[1,2,2],[2,1,2],[2,2,1]][[1,2,2],[2,1,2],[2,2,1]]`
`=[[1xx1+2xx2+2xx2,1xx2+2xx2+2xx2,1xx2+2xx2+2xx1],[2xx1+1xx2+2xx2,2xx2+1xx1+2xx2,2xx2+1xx2+2xx1],[2xx1+2xx2+1xx2,2xx2+2xx1+1xx2,2xx2+2xx2+1xx1]]`
`=[[1+4+4,2+2+4,2+4+2],[2+2+4,4+1+4,4+2+2],[2+4+2,4+2+2,4+4+1]]`
`=[[9,8,8],[8,9,8],[8,8,9]]`
consider A2-4A-5I
`=[[9,8,8],[8,9,8],[8,8,9]]-4[[1,2,2],[2,1,2],[2,2,1]]-5[[1,0,0],[0,1,0],[0,0,1]]`
`=[[9,8,8],[8,9,8],[8,8,9]]-[[4,8,8],[8,4,8],[8,8,4]]-[[5,0,0],[0,5,0],[0,0,5]]`
`=[[9-9,8-8,8-8],[8-8,9-9,8-8],[8-8,8-8,9-9]]`
`=[[0,0,0],[0,0,0],[0,0,0]]`
Now
A2-4A-5I=0
A2-4A=5I
`A^2A^(-1)-4A.A^(-1)=5IA^(-1)` (Postmultiply by A-1)
A-4I=5A-1
`[[1,2,2],[2,1,2],[2,2,1]]-[[4,0,0],[0,4,0],[0,0,4]]=5A^-1`
`[[-3,2,2],[2,-3,2],[2,2,-3]]=5A^(-1)`
`A^-1 =[[-3/5,2/5,2/5],[2/5,-3/5,2/5],[2/5,2/5,-3/5]]`
APPEARS IN
RELATED QUESTIONS
if `A=[[2,0,0],[0,2,0],[0,0,2]]` then A6= ......................
Solve the following matrix equation for x: `[x 1] [[1,0],[−2,0]]=0`
If `A=([2,0,1],[2,1,3],[1,-1,0])` find A2 - 5A + 4I and hence find a matrix X such that A2 - 5A + 4I + X = 0
Compute the following:
`[(a,b),(-b, a)] + [(a,b),(b,a)]`
Compute the following:
`[(a^2+b^2, b^2+c^2),(a^2+c^2, a^2+b^2)] + [(2ab , 2bc),(-2ac, -2ab)]`
Compute the following:
`[(cos^2x, sin^2 x),(sin^2 x ,cos^2 x)]+[(sin^2 x, cos^2 x), (cos^2 x, sin^2 x)]`
Compute the following sums:
`[[3 -2],[1 4]]+ [[-2 4 ],[1 3]]`
Let A = `[[2,4],[3,2]]`, `B=[[1,3],[-2,5]]`and `c =[[-2,5],[3,4]]`.Find each of the following: 2A − 3B
Let A = `[[2,4],[3,2]]`, `B=[[1,3],[-2,5]]`and `c =[[-2,5],[3,4]]`.Find each of the following: 3A − C
Let A = `[[2,4],[3,2]]`, `B=[[1,3],[-2,5]]`and `c =[[-2,5],[3,4]]`.Find each of the following: 3A − 2B + 3C
If A =`[[2,3],[5,7]],B =` `[[-1,0 ,2],[3,4,1]]`,`C= [[-1,2,3],[2,1,0]]`find : A + B and B + C
If A =`[[2 3],[5 7]],B =` `[[-1 0 2],[3 4 1]]`,`C= [[-1 2 3],[2 1 0]]`find
2B + 3A and 3C − 4B
If A = diag (2 − 59), B = diag (11 − 4) and C = diag (−6 3 4), find
B + C − 2A
Find matrices X and Y, if 2X − Y = `[[6 -6 0],[-4 2 1]]`and X + 2Y =`[[3 2 5],[-2 1 -7 ]]`
f X − Y =`[[1 1 1],[1 1 0],[1 0 0]]` and X + Y = `[[3 5 1],[-1 1 1],[11 8 0]]`find X and Y.
If A =`[[9 1],[7 8]],B=[[1 5],[7 12]]`find matrix C such that 5A + 3B + 2C is a null matrix.
If A = `[[2 -2],[4 2],[-5 1]],B=[[8 0],[4 -2],[3 6]]`
, find matrix X such that 2A + 3X = 5B.
If A = `[[1 -3 2],[2 0 2]]`and `B = [[2 -1 -1],[1 0 -1]]` find the matrix C such that A + B + C is
, find the matrix C such that A + B + C is zero matrix.
Find x, y satisfying the matrix equations
`[[X-Y 2 -2],[4 x 6]]+[[3 -2 2],[1 0 -1]]=[[ 6 0 0],[ 5 2x+y 5]]`
Find x, y satisfying the matrix equations
`x[[2],[1]]+y[[3],[5]]+[[-8],[-11]]=0`
If 2 `[[3 4],[5 x]]+[[1 y],[0 1]]=[[7 0],[10 5]]` find x and y.
Find the value of λ, a non-zero scalar, if λ
Find a matrix X such that 2A + B + X = O, where
If A = `[[8 0],[4 -2],[3 6]]` and B = `[[2 -2],[4 2],[-5 1]]`
, then find the matrix X of order 3 × 2 such that 2A + 3X = 5B.
Find x, y, z and t, if
`3[[x y],[z t]]=[[x 6],[-1 2t]]+[[4 x+y],[z+t 3]]`
Find x, y, z and t, if
`2[[x 5],[z t]]+[[x 6],[-1 2t]]=[[7 14],[15 14]]`
If X and Y are 2 × 2 matrices, then solve the following matrix equations for X and Y.
`2X + 3Y = [[2,3],[4,0]], 3X+2Y = [[-2,2],[1,-5]]`
Express the matrix \[A = \begin{bmatrix}3 & - 4 \\ 1 & - 1\end{bmatrix}\] as the sum of a symmetric and a skew-symmetric matrix.
If \[A = \begin{bmatrix}\cos x & \sin x \\ - \sin x & \cos x\end{bmatrix}\] , find x satisfying 0 < x < \[\frac{\pi}{2}\] when A + AT = I
If A = [aij] is a skew-symmetric matrix, then write the value of \[\sum_i \sum_j\] aij.
If \[\binom{x + y}{x - y} = \begin{bmatrix}2 & 1 \\ 4 & 3\end{bmatrix}\binom{1}{ - 2}\] , then write the value of (x, y).
If \[I = \begin{bmatrix}1 & 0 \\ 0 & 1\end{bmatrix}, J = \begin{bmatrix}0 & 1 \\ - 1 & 0\end{bmatrix} and B = \begin{bmatrix}\cos \theta & \sin \theta \\ - \sin \theta & \cos \theta\end{bmatrix}\] then B equals )
Addition of matrices is defined if order of the matrices is ______.
If A = `[(2, 1)]`, B = `[(5, 3, 4),(8, 7, 6)]` and C = `[(-1, 2, 1),(1, 0, 2)]`, verify that A(B + C) = (AB + AC).
Let A = `[(1, 2),(-1, 3)]`, B = `[(4, 0),(1, 5)]`, C = `[(2, 0),(1, -2)]` and a = 4, b = –2. Show that: A + (B + C) = (A + B) + C
Let A = `[(1, 2),(-1, 3)]`, B = `[(4, 0),(1, 5)]`, C = `[(2, 0),(1, -2)]` and a = 4, b = –2. Show that: (a + b)B = aB + bB
If A = `[(0, -x),(x, 0)]`, B = `[(0, 1),(1, 0)]` and x2 = –1, then show that (A + B)2 = A2 + B2.
Matrix multiplication is ______ over addition.
`"A" = [(1,-1),(2,-1)], "B" = [("x", 1),("y", -1)]` and (A + B)2 = A2 + B2, then x + y = ____________.
If `[(2"a"+"b", "a"-2"b"),(5"c" - "d", 4"c"+3"d")] = [(4, -3),(11, 24)]`, then value of a + b – c + 2d is:
Let A = `[(1, -1),(2, α)]` and B = `[(β, 1),(1, 0)]`, α, β ∈ R. Let α1 be the value of α which satisfies (A + B)2 = `A^2 + [(2, 2),(2, 2)]` and α2 be the value of α which satisfies (A + B)2 = B2 . Then |α1 – α2| is equal to ______.
