Day 116 and 117 – March 1, 2

Algebra 1a: Chapter 8, Lesson 3, page 367.

Addition and Subtraction for 2 linear equations.

You can add 2 (or subtract) linear equations together so that one of the variables cancels out. An example would be:

`3x – y = 9` and `2x + y = 6`

If we line them up, one under the other, we have:

`3x – y = 9`

`2x + y = 6`

Adding them together, we see that the sum looks like `3x + 2x – y + y = 9 + 6`

or

`5x = 15`

and solving for `x` makes it `x = 3`. If `x = 3`, then we can plug it into EITHER original equation, I’ll use the second one and we can solve for `y`.

So…  `2x + y = 6`

becomes `2*3 + y = 6` or `6 + y = 6` or `y = 0`. The ordered pair solution is then `(3, 0)`!

We may sometimes have to scale (multiply) ONE OR BOTH of the equations to make one of the variables disappear. Here is a link that can help!

Two of tonight’s homework problems solved by MrE are here! Just click it!

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