Algebra

I have a question about using the addition method for the following problem:
4x-5y=7
-4x+5y=7

Since both variables are cancelled out what do you do to find the point of intersection? 0?

4reading said:

I have a question about using the addition method for the following problem:
4x-5y=7
-4x+5y=7

Since both variables are cancelled out what do you do to find the point of intersection? 0?

Click to expand...

When you add the two equations together, you get this:

0 = 14

Now, when is THAT true? It's never true that 0 = 14, so that tells you that there is NO ordered pair (x, y) which will make both equations true at the same time. In other words, these lines do not intersect.

To see why, solve each equation for y to get the equation in slope-intercept form. Then look at the slopes for the two lines....several days ago, you had a question in which the two equations had the same slope. Remember what I told you then?

Re: Algebra for 4x + -5 =7

Simplifying
4x + -5y = 7

Solving
4x + -5y = 7

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '5y' to each side of the equation.
4x + -5y + 5y = 7 + 5y

Combine like terms: -5y + 5y = 0
4x + 0 = 7 + 5y
4x = 7 + 5y

Divide each side by '4'.
x = 1.75 + 1.25y

Simplifying
x = 1.75 + 1.25y