Question

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

Answer 1

y=-2x 
We know this because the slope is -2 (slope is found using rise/run, in this case the rise is 2 and the run is -1, so 2/-1=-2), and the y-intercept is at 0 (the y-intercept is the point at which a line crosses the y-axis).

:)

Answer 2

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