- #1

cepheid

Staff Emeritus

Science Advisor

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## Main Question or Discussion Point

I understand why two of the three row operations do not change the solution set of a system:

1. Interchange two rows. (Doesn't make much difference in what order one decides to write down the linear equations does it?)

2. Multiply a row by a scalar. (This step doesn't change the solution set because e.g. writing 2x = 6 instead of x = 3 doesn't change the geometric situation at all)

It's the third one that's giving me trouble:

3. Replace one row with the sum of it and a multiple of another row.

Even though this is the key method of solving simultaneous equations, I cannot justify to myself that it doesn't change the solution set of a system. Can anyone shed light on this?

1. Interchange two rows. (Doesn't make much difference in what order one decides to write down the linear equations does it?)

2. Multiply a row by a scalar. (This step doesn't change the solution set because e.g. writing 2x = 6 instead of x = 3 doesn't change the geometric situation at all)

It's the third one that's giving me trouble:

3. Replace one row with the sum of it and a multiple of another row.

Even though this is the key method of solving simultaneous equations, I cannot justify to myself that it doesn't change the solution set of a system. Can anyone shed light on this?