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If A is any mxn such that AB and BA are both defined show that B is an mxn matrix?
Wiki User
∙ 9y ago
By rule of matrix multiplication the number of rows in the first matrix must equal the number of rows in the second matrix. If A is an axb matrix and B is a cxd matrix, then a = d. Then if BA is defined, then c = b. This means that B is not necessarily mxn, but must be nxm.
Wiki User
∙ 9y ago
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To square a matrix, simply multiply the matrix by itself. It is just like squaring any other regular number in mathematics.
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First, we need to recall that a linear equation does not involve any products or roots of variables. All variables occur only to the first power and do not appear as arguments for trigonometric, logarithmic, or exponential functions. For example, x + √y = 4, y = sin x, and 2x + y - z + yz = 5 are not linear.To solve a system of equations such as3x + y = 52x - y = 3all information required for the solution is emboded in the augmented matrix (imagine that I put those information into a rectangular arrays)3 1 52 -1 3and that the solution can be obtained by performing appropriate operations on this matrix.The matrix of this system linear equations is a square matrix A such as3 12 -1Think this matrix asa bc dTo find an inverse of this square matrix A (2 x 2), we need to find a matrix B of the same size such that AB = I and BA = I, then A is said to be invertible and B is called the inverse of A. If no such a matrix can be found, then A is said to be singular.An invertible matrix has exactly one inverse.A square matrix A is invertible if ad - bc ≠ 0 (where ad - bc is the determinant)The formula of finding the inverse of a square matrix A isA-1 = [1/(ad - bc)][d -b the second row -c a](I'm sorry, I can't draw the arrays)So let's find the inverse of our example.A-1 = [1/(-3 -2)][-1 -1 the second row -2 3] = [-1/-5 -1/-5 the sec. row -2/-5 3/-5] =1/5 1/52/5 -3/5A n x m matrix cannot have an inverse. A n x n matrix may or may not have an inverse.To find the inverse of a n x n matrix we should to adjoin the identity matrix to the right side of A, thereby producing a matrix of the form [A | I]. Then we should apply row opperations to this matrix until the left side is reduced to I. This opperations will convert the right side to A-1, so the final matrix will have the form [I |A-1 ].(There are many other methods how to find the inverse of a n x n matrix, but I can't show them by examples. I am so sorry that I can't be so much useful to you).
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A singular matrix is a matrix that is not invertible. If a matrix is not invertible, then:• The determinant of the matrix is 0.• Any matrix multiplied by that matrix doesn't give the identity matrix.There are a lot of examples in which a singular matrix is an idempotent matrix. For instance:M =[1 1][0 0]Take the product of two M's to get the same M, the given!M x M = MSo yes, SOME singular matrices are idempotent matrices! How? Let's take a 2 by 2 identity matrix for instance.I =[1 0][0 1]I x I = I obviously.Then, that nonsingular matrix is also idempotent!Hope this helps!
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