Answer:
[tex]X= \left[\begin{array}{ccc}-4&1\\5&-1\\\end{array}\right] \left[\begin{array}{ccc}21\\20\\\end{array}\right] \\[/tex]
Step-by-step explanation:
Given the simultaneous equation
x+y=21
5x+4y=20
To write in matrix form, it must be in the form AX= b
X = A⁻¹b
A⁻¹ is the inverse of matrix A
A is a 2by2 matrix
X is the variables
b is a column matrix
The expression will therefore be written as;
[tex]A=\left[\begin{array}{ccc}1&1\\5&4\\\end{array}\right] \\\\|A| = 1(4)- 5(1)\\|A| = 4-5\\|A| = -1\\A^{-1} = -\left[\begin{array}{ccc}4&-1\\-5&1\\\end{array}\right] \\\\A^{-1} = \left[\begin{array}{ccc}-4&1\\5&-1\\\end{array}\right] \\[/tex]
Hence the required product matrix that represent X is;
[tex]X= \left[\begin{array}{ccc}-4&1\\5&-1\\\end{array}\right] \left[\begin{array}{ccc}21\\20\\\end{array}\right] \\[/tex]
