Question #82857

Solve the following equations using matrix algebra:

2x + y - z = 11

x - 2y + 2z = -2

3x - y + 3z = 5

Expert's answer

Answer on Question #82857 - Math - Linear Algebra

1. We present the equation in the form of a 3 by 3 matrix:


[2111112223135]\left[ \begin{array}{cccc} 2 & 1 & -1 & | & 11 \\ 1 & -2 & 2 & | & -2 \\ 3 & -1 & 3 & | & 5 \end{array} \right]


2. For convenience, we change the 1st and second line:


[1222211113135]\left[ \begin{array}{cccc} 1 & -2 & 2 & | & -2 \\ 2 & 1 & -1 & | & 11 \\ 3 & -1 & 3 & | & 5 \end{array} \right]


3. Multiply the 1st row by -2 and -3 and add to the second and third row respectively:


[12220551505311]\left[ \begin{array}{cccc} 1 & -2 & 2 & | & -2 \\ 0 & 5 & -5 & | & 15 \\ 0 & 5 & -3 & | & 11 \end{array} \right]


4. Multiply the 2nd row by -1 and add to the 3rd. Divide the 2nd line by 5:


[122201130024]\left[ \begin{array}{cccc} 1 & -2 & 2 & | & -2 \\ 0 & 1 & -1 & | & 3 \\ 0 & 0 & 2 & | & -4 \end{array} \right]


5. Divide the 3rd line by 2:


[122201130012]\left[ \begin{array}{cccc} 1 & -2 & 2 & | & -2 \\ 0 & 1 & -1 & | & 3 \\ 0 & 0 & 1 & | & -2 \end{array} \right]


6. Add the third line to the second. Multiply the 3rd row by -2 and add to 1st:


[120201010012]\left[ \begin{array}{cccc} 1 & -2 & 0 & 2 \\ 0 & 1 & 0 & 1 \\ 0 & 0 & 1 & -2 \end{array} \right]


7. Multiply the 2nd row by 2 and add to 1st:


[100401010012]\left[ \begin{array}{cccc} 1 & 0 & 0 & 4 \\ 0 & 1 & 0 & 1 \\ 0 & 0 & 1 & -2 \end{array} \right]


Answer:


{x=4y=1z=2\left\{ \begin{array}{l} x = 4 \\ y = 1 \\ z = -2 \end{array} \right.


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