Respuesta :

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]

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