Question

For the following system, if you isolated x in the first equation to use the Substitution Method, what expression would you substitute into the second equation?

-x + 2y = -6
3x + y = 8

Answer 1

-2y + 6

2y - 6

2y + 6

-2y - 6

Answer 2

Let's solve the first equation for x.

Answer 3

You want x alone.
First, subtract 2y from both sides. What do you get?

Answer 4

Normally you would isolate y. I would do that if you could, but if the question is specific to isolating x, then sorry.

Answer 5

@emilycs713
There is no rule that you normally would isolate y. You isolate whichever variable you feel like, unless you're asked specifically to isolate one of them, like in this problem.

Answer 6

It's true, there is no rule to isolate y, but that is the normal stance you would take to solve an equation, which is why I was surprised by this one. It is no problem to solve for x, but it could complicate the process.

Answer 7

There is no rule, and isolating y is not the normal stance. You should look at each problem and find the equation that is easiest to solve for either variable and solve for that variable. The normal stance is make it the easiest and quickest possible.

Answer 8

For example, in this problem, if I were asked to solve by substitution, but without specifying which variable of which equation to solve for first, I would have solved for y in the second equation, since that is the easiest one-step process there is in this system.

Answer 9

So what's the answer?

Answer 10

I asked you to do a simple step in solving. Would you like to try it?

Answer 11

Subtract 2y from both sides. I set it up for you.

-x + 2y = -6
- 2y - 2y
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Answer 12

-x = -2y - 6

Now multiply both sides by -1:

x = 2y + 6