Posted by **Neil** on Wednesday, October 3, 2012 at 3:31pm.

Solve by using the subatitution method. (Please keep fractions as they are, don't convert to decimal.)

1. y= -3x - 1

2x - 3y= -8

2. 1 + 3y= 10

5x + 2y= 6

3. 2x - 6y= -2

x= 3y - 1

4. y= 1/7x + 3

x - 7y= -4

- Math -
**Reiny**, Wednesday, October 3, 2012 at 3:43pm
I will do #3, you try the others

3.

2x - 6y = -2

x = 3y-1

sub into the 1st:

2(3y-1) - 6y = -2

6y - 2 - 6y = -2

0 = 0

Ahhh, since the variables dropped out and we ended up with a TRUE statement, the two equations are really one and the same equation.

(if you simplify the first, you get the second ...

2x - 6y = -2

divide by 2

x - 3y = -1

x = 3y - 1, which was the second equation )

So any ordered pair which satisfies the 1st will obviously also satisfy the second.

Had we ended up with a false statement, such as 3 = 0, there would have been no solution at all

- Math -
**Neil**, Wednesday, October 3, 2012 at 4:05pm
Hm... so, 0=0 is the only answer for #3? You don't have to do anything else? Like plugging in for the second equation or something.

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