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What is a Line?

Check out one more example:

Is the point ( -2.5, .7 ) on the line x - 2y = -4 ?

a graph of the line x - 2y = -4 and the point ( -2.5, .7 ) showing that the point LOOKS like it might be ON the line

We'll need to do the algebra:

x - 2y = -4 which gives us (-2.5) - 2(.7) = -4 which gives us -2.5 - 1.4 = -4 which gives us -3.9 = -4 ?

Doh!  Close, but it just isn't happening!

So, the point ( -2.5, .7 ) is NOT on the line x - 2y = -4

The key is to ALWAYS use algebra to really be sure!
 

YOUR TURN:

Without graphing, see if the given point lies on the given line:

( -1, -3 ) and x + y = -4

( .5, .5 ) and 3x - y = 1

( -4, 3.5 ) and 2x + 5y = 10

When you learn how to graph lines, you should come back and see what the graphs look like too.