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Find the inverse of \(A^{2}\) and the inverse of \(A^{3}\) (where \(A^{2}\) is the product AA and \(A^{3}\) is the product \(\left(A^{2}\right) A\) ). $$A=\left[\begin{array}{ll}1 & 0 \\\2 & 1\end{array}\right]$$

Short Answer

Expert verified
The inverse of \(A^2\) is \( (A^2)^{-1} = \begin{bmatrix} 1 & 0 \\ -2 & 1 \end{bmatrix}\) and the inverse of \(A^3\) is \( (A^3)^{-1} = \begin{bmatrix} 1 & 0 \\ -2 & 1 \end{bmatrix}\)

Step by step solution

01

Find the inverse of A

The formula to calculate the inverse of a 2x2 matrix \( A = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \) is \(A^{-1} = \frac{1}{ad-bc} \begin{bmatrix} d & -b \\ -c & a \end{bmatrix}\). Applying this formula, the inverse of the given matrix A is \(A^{-1} = \begin{bmatrix} 1 & 0 \\ -2 & 1 \end{bmatrix}\)
02

Calculate the square of A and its inverse

The square of A is identical to A as the product of A and A is\( A^2 = \begin{bmatrix} 1 & 0 \\ 2 & 1 \end{bmatrix}\). Using the same formula as step 1, the inverse of \(A^2\) is \( (A^2)^{-1} = \begin{bmatrix} 1 & 0 \\ -2 & 1 \end{bmatrix}\)
03

Calculate the cube of A and its inverse

The cube of A is similarly identical to A as the product of \(A^2\) and A is \(A^3 = \begin{bmatrix} 1 & 0 \\ 2 & 1 \end{bmatrix}\). Using the same formula, the inverse of \(A^3\) is \( (A^3)^{-1} = \begin{bmatrix} 1 & 0 \\ -2 & 1 \end{bmatrix}\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Inverse of a Matrix
The inverse of a matrix is akin to the reciprocal of a number. For a matrix to have an inverse, it must be a square matrix, and not every square matrix is guaranteed to have one. The inverse of a matrix, when multiplicated with the original matrix, yields the identity matrix, which plays a role similar to '1' in regular multiplication.

For a 2x2 matrix, the inverse can be calculated using the formula \[\begin{equation}A^{-1} = \frac{1}{ad-bc} \begin{bmatrix}d & -b \ -c & a\end{bmatrix}\end{equation}\], where \( a, b, c, d \) are elements of the matrix \( A = \begin{bmatrix}a & b \ c & d\end{bmatrix} \). The denominator \( ad-bc \) is the determinant of the matrix, and it is crucial that this value is non-zero; otherwise, the matrix does not have an inverse.

To improve understanding, it's important to further explore an example. If we have a matrix \( A = \begin{bmatrix}1 & 0 \ 2 & 1\end{bmatrix} \), to find its inverse, we apply the steps outlined above. Since the determinant \( ad-bc = (1)(1)-(0)(2) = 1 \), which is non-zero, the inverse \( A^{-1} \) thus becomes \( \begin{bmatrix}1 & 0 \ -2 & 1\end{bmatrix} \). When you multiply \( A \) by \( A^{-1} \), the result should yield the identity matrix, confirming the correctness of the inverse calculation.
Matrix Operations
Matrix operations, like those for numbers, include addition, subtraction, multiplication, and finding inverses. It's essential to understand that these operations have certain conditions and properties. For instance, matrices must be of the same dimensions to be added or subtracted.

When it comes to matrix multiplication, it is not commutative, which means the order in which you multiply matrices matters significantly. The product of two matrices is possible when the number of columns in the first matrix equals the number of rows in the second matrix.

In our exercise example where \( A = \begin{bmatrix}1 & 0 \ 2 & 1\end{bmatrix} \), multiplying A by itself to get \( A^{2} \) or by \( A^{2} \) to get \( A^{3} \) showcases matrix multiplication. It is also to note that finding the inverse of a matrix, \( A^{-1} \), is another operation, which has its distinct rules. One crucial takeaway here is that the inverse of a product of matrices, provided they are invertible, is the product of their inverses in the reverse order; i.e., \( (AB)^{-1} = B^{-1}A^{-1} \).
Properties of Matrix Exponents
Exponents with matrices work somewhat differently from the way we understand exponents with numbers. With matrices, when you raise a matrix to a power, you multiply the matrix by itself a certain number of times as indicated by the exponent. This brings us to a fundamental property: the exponentiation of a matrix is only defined for square matrices.

Another property is that for any non-singular square matrix A, \( A^{0} \) is defined as the identity matrix of the same order. Moreover, for integer exponents, \( A^{m}A^{n} = A^{m+n} \) and \( (A^{m})^{n} = A^{mn} \), where m and n are integers, hold true under the condition that matrix multiplication is possible.

In the given exercise, calculating \( A^{2} \) and \( A^{3} \) is straightforward since A is a square matrix. Additionally, the fact that \( A^{2} \) and \( A^{3} \) yield the same matrix as A is an interesting consequence of the particular matrix in question, and not a general property of exponents with matrices. Normally, these operations would change the matrix. Furthermore, the inverse of \( A^{n} \), where n is a positive integer, is equal to \( (A^{-1})^{n} \), because repeatedly multiplying a matrix by its inverse still gives the identity matrix.

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Most popular questions from this chapter

Apply elementary row operations to a matrix to solve the system of equations. If there is no solution, state that the system is inconsistent. $$\left\\{\begin{array}{c}x+2 y+z=-3 \\ 3 x+y-2 z=2 \\ 4 x+3 y-z=0\end{array}\right.$$

Apply elementary row operations to a matrix to solve the system of equations. If there is no solution, state that the system is inconsistent. $$\left\\{\begin{aligned} x+3 y &=2 \\ 5 x+12 y+3 z &=1 \\\\-4 x-9 y-3 z &=1 \end{aligned}\right.$$

A furniture manufacturer makes three different picces of furniture, each of which utilizes some combination of fabrics \(A, B,\) and \(C .\) The yardage of each fabric required for each piece of furniture is given in matrix \(F\). Fabric A Fabric B Fabric C (yd) \(\quad\) (yd) \(\quad\) (yd) \(\begin{array}{r}\text { Sofa } \\ \text { Loveseat } \\ \text { Chair }\end{array}\left[\begin{array}{ccc}10.5 & 2 & 1 \\ 8 & 1.5 & 1 \\ 4 & 1 & 0.5\end{array}\right]=F\) The cost of each fabric (in dollars per yard) is given in matrix \(C\).$$\begin{array}{l}\text { Fabric A } \\\\\text { Fabric B } \\\\\text { Fabric C }\end{array}\left[\begin{array}{r}10 \\\6 \\\5\end{array}\right]=C$$ Find the total cost of fabric for each piece of furniture.

Consider the following augmented matrix. For what value(s) of \(a\) does the corresponding system of linear equations have infinitely many solutions? One solution? Explain your answers.$$\left[\begin{array}{lll|r}1 & 0 & 0 & -2 \\\0 & 1 & 0 & 5 \\\0 & 0 & a & 0\end{array}\right]$$.

The area of a rectangular property is 1800 square feet; its length is twice its width. There is a rectangular swimming pool centered within the property. The dimensions of the property are one and onethird times the corresponding dimensions of the pool. The portion of the property that lies outside the pool is paved with concrete. What are the dimensions of the property and of the pool? What is the area of the paved portion?

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