Eric C. answered • 02/07/20

Math and Physics Expert with 20+ years teaching experience

There are three elementary row operations:

a) interchange two rows

b) multiply a row by a constant

c) add a constant multiple of one row to another row

In this problem, they are asking you to perform the third operation. You are being asked to replace equation 3 with the sum of equations 1 and 3. Thus, the first two equations will be unchanged, but the third equation should be replaced by:

(-x + y - z = 10) + (x + 2y + z = 5) => 0x + 3y +0z = 15 => y = 5

I hope this helps.