Matthew P. answered • 09/15/19

Computer Science Student Who Loves Teaching Math

Hi there!

For this problem, it looks like we'll want to perform some row reducing, but only in relation to that one entry so as to make every other entry in that column 0. The first step, as it looks like you've already done, is to multiply the second row by -1/2:

1 -9 -5 | -4 1 -9 -5 | -4

0 -2 - 4 | 7 → 0 1 2 | -7/2

0 -9 1 | -9 0 -9 1 | -9

From here, we'll then want to perform row operations on rows 1 and 3 to make their second entries 0:

R_{1} + 9R_{2}

R_{3} + 9R_{2}

So we calculate:

1 -9 -5 | -4 1 0 13 | -71/2

0 1 2 | -7/2 → 0 1 2 | -7/2

0 -9 1 | -9 0 0 19 | -81/2

And there you have your missing values. I hope this helped, and please let me know if you're still confused!

*sorry if the matrices are poorly formatted, they're way harder to write than I first thought.