If A=[xy5−8] determine the values of x and y for which A2=A.

Given the 2 by 2 matrix [tex]A = \left[\begin{array}{-cc}x&5\\y&-8\\\end{array}\right][/tex] , we are to find the value of x and y for the expression A² = A to be true.

First we need to find A² by multiplying the same matrix together

[tex]A^2 = \left[\begin{array}{-cc}x&5\\y&-8\\\end{array}\right] \left[\begin{array}{-cc}x&5\\y&-8\\\end{array}\right]\\\\ \ we \ normally \ multiply \ the \ rows \ of \ the \ first \ matrix \ with \ the \ column \ of \ the \ second \\\\A^2 = \left[\begin{array}{-cc}x^2+5y&5x-40\\xy-8y&5y+64\\\end{array}\right]\\\\Since \ A^2 = A,\ hence;\\\\\left[\begin{array}{-cc}x^2+5y&5x-40\\xy-8y&5y+64\\\end{array}\right] = \left[\begin{array}{-cc}x&5\\y&-8\\\end{array}\right]\\[/tex]

Equating the first row and second column of both matrices together, we will have;

5x-40 = 5

add 40 to both sides of the equation

5x-40+40 = 5+40

5x = 45

x = 45/5

x = 9

Similarly, we will equate the second row and second column of both matrices to have;

5y+64 = -8

Subtract 64 from both sdies

5y+64-64 = -8-64

5y = -72

y = -72/5

Hence the value of x is 9 and y is -72/5

MrRoyal MrRoyal · Answer 2 · 2021-10-25T04:04:14+02:00

Matrices are used to represent data in rows and columns

The values of x and y are 9 and -14.4 respectively.

Matrix A is represented as:

[tex]\mathbf{A = \left[\begin{array}{ccc}x&5\\y&-8\end{array}\right] }[/tex]

Calculate [tex]\mathbf{A^2}[/tex]

[tex]\mathbf{A^2 = \left[\begin{array}{ccc}x&5\\y&-8\end{array}\right] \times \left[\begin{array}{ccc}x&5\\y&-8\end{array}\right] }[/tex]

Recall that [tex]\mathbf{A^2 = A}[/tex]

This means that:

[tex]\mathbf{\left[\begin{array}{ccc}x^2++5y&5x-40\\xy-8y&5y+64\end{array}\right] = \left[\begin{array}{ccc}x&5\\y&-8\end{array}\right] }[/tex]

So, by comparison

[tex]\mathbf{5x - 40 = 5}[/tex]

[tex]\mathbf{5x = 40 + 5}[/tex]

[tex]\mathbf{5x = 45}[/tex]

[tex]\mathbf{x = 9}[/tex]

Similarly

[tex]\mathbf{5y + 64 = -8}[/tex]

[tex]\mathbf{5y =-64 -8}[/tex]

[tex]\mathbf{5y =-72}[/tex]

[tex]\mathbf{y =-14.4}[/tex]

Hence, the values of x and y are 9 and -14.4 respectively.