Which rule matches the function graphed below?
y= - 2x.
y= x+4
y = 2x
y = x -4

Take any two points to find the slope of a line.  The slope will be equal to:

(y2-y1)/(x2-x1) and any two points will do...

I'll use (-2,4) and (0,0) :P so the slope is:

(0-4)/(0--2)=-4/2=-2, now we know the slope is -2 so:

y=-2x+b  (now we know b=0, but I'll use another point anyway to solve for b)

Let's use (-2,4) again...

4=-2(-2)+b

4=4+b

b=0

So the line is:

y=-2x