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What if we want to graph this?

y = -2

Hmm... It doesn't look like there's enough there!

Where's the x?  We're used to these:

Ax + By = C and y = mx + b

Well, here's the deal:

If the x isn't there, then it can be anything!

And y is locked in at -2.

So, what would this look like?
 

It's a horizontal line! ... the graph of y = -2 is a line that goes straight across ... and x can be anything! ... the line goes through the points ( -1, -2 ) and ( 0 , -2 )
 

So, what's the slope of this line?  Grab two points and see?

m = ( y2 - y1 ) / ( x2 - x1 ) = -2 - ( -2 ) / -1 - 0 = 0 / -1 = 0

The slope of a horizontal line is 0!

Since it's always hard to remember when these guys are horizontal and when they are vertical, I've got a sentence that will always save you...

When you see y = -2, say this:

y is always -2 and x can be anything!

This tells you what the graph should look like!


TRY IT:

Graph y = 1

... Then, grab two points and find the slope.