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Perform the row operation on the given augmented matrix.

[tex]\[
\left[\begin{array}{rrr|r}
1 & 1 & -9 & -4 \\
9 & 6 & 8 & 1 \\
-5 & 6 & 7 & 4
\end{array}\right] \quad R_2 = -9R_1 + R_2
\][/tex]


Sagot :

Sure, let's go through the detailed steps to perform the row operation [tex]\( R_2 = -9R_1 + R_2 \)[/tex] on the given augmented matrix:

[tex]\[ \left[\begin{array}{rrr|r} 1 & 1 & -9 & -4 \\ 9 & 6 & 8 & 1 \\ -5 & 6 & 7 & 4 \end{array}\right] \][/tex]

### Step 1: Identify the Row Operation
We're instructed to perform the row operation on the second row [tex]\( R_2 \)[/tex]:

[tex]\[ R_2 = -9R_1 + R_2 \][/tex]

### Step 2: Multiply [tex]\( R_1 \)[/tex] by [tex]\(-9\)[/tex]
First, we need to multiply each element of the first row ([tex]\( R_1 \)[/tex]) by [tex]\(-9\)[/tex]:

[tex]\[ R_1 = \left[\begin{array}{rrrr} 1 & 1 & -9 & -4 \end{array}\right] \][/tex]

[tex]\[ -9 \times R_1 = \left[\begin{array}{rrrr} -9 \times 1 & -9 \times 1 & -9 \times (-9) & -9 \times (-4) \end{array}\right] = \left[\begin{array}{rrrr} -9 & -9 & 81 & 36 \end{array}\right] \][/tex]

### Step 3: Add the Result to [tex]\( R_2 \)[/tex]
Now, we add this result to the elements of the second row [tex]\( R_2 \)[/tex]:

[tex]\[ R_2 = \left[\begin{array}{rrrr} 9 & 6 & 8 & 1 \end{array}\right] \][/tex]

[tex]\[ R_2 = -9R_1 + R_2 = \left[\begin{array}{rrrr} -9 & -9 & 81 & 36 \end{array}\right] + \left[\begin{array}{rrrr} 9 & 6 & 8 & 1 \end{array}\right] \][/tex]

Combining the elements, we get:

[tex]\[ R_2 = \left[\begin{array}{rrrr} -9 + 9 & -9 + 6 & 81 + 8 & 36 + 1 \end{array}\right] = \left[\begin{array}{rrrr} 0 & -3 & 89 & 37 \end{array}\right] \][/tex]

### Step 4: Substitute Back into the Matrix
Finally, we substitute the new [tex]\( R_2 \)[/tex] back into the original matrix:

[tex]\[ \left[\begin{array}{rrr|r} 1 & 1 & -9 & -4 \\ 0 & -3 & 89 & 37 \\ -5 & 6 & 7 & 4 \end{array}\right] \][/tex]

Thus, after performing the row operation [tex]\( R_2 = -9R_1 + R_2 \)[/tex], the augmented matrix becomes:

[tex]\[ \left[\begin{array}{rrr|r} 1 & 1 & -9 & -4 \\ 0 & -3 & 89 & 37 \\ -5 & 6 & 7 & 4 \end{array}\right] \][/tex]