# Finding intersections

1. Sep 27, 2004

### bob4000

i need some help with the following:

i know how to calculate the intersections when an equation like 3x+4y=33, y=x-1. but what do i do when y=x-1 becomes 2y=x-1; all of this using the substitution method. thnx

2. Sep 27, 2004

### Muzza

If 2y = x - 1 then y = (x - 1)/2 = 0.5x - 0.5.

3. Sep 27, 2004

### bob4000

thts what thought but it doesnt seem to correlate with the answers in the textbook. i'll try again. thnx all the same

4. Sep 27, 2004

### pig

There are two simple ways to substitute.

First, you can add 1 to both sides of the second equation:
2y + 1 = x - 1 + 1
2y + 1 = x
So now you can substitute 2y+1 instead of x in the first equation.

Another way would be to multiply both sides with 1/2:
2y * 1/2 = (x - 1) * 1/2
y = (x-1)/2
Now you can substitute (x-1)/2 instead of y.

Remember, you are allowed to add the same number to both sides, and to multiply both sides with the same number.

5. Sep 27, 2004

### bob4000

i jus thought tht it wud be a little bit more complicated, but thnx all the same, jus needed to make sure i was on the right track.