whats the equation for (0,-1)(2,-5)(4,-9)

Question

I know the -1 crosses at on the y-axis, I just cant seem to find the equation to the points

 

Answer 1

You probably know that the standard slope-intercept form for a line is y = mx + b, where m is the slope and b is the y-intercept. From what you say in your question, you know that b = -1. This is very good, so we have y = mx - 1; now, what's m?

Slope is rise over run; from the second point you provided, we can draw a line between the first and second points ((0, -1) and (2, -5) respectively). We therefore get an m-value of (-5-(-1))/(2-0) or -4/2 or -2. The same answer will be obtained if you check the second and third points (which I won't go into any more detail here), so the line's equation is y = -2x + 1.

Answer 2

These three points are co-linear. Therefore, the equation can be found based on any two of the three points.

Picking the first two points,

slope = m = (-1+5)/(0-2) = -2

y-intercept = b = -1

y = mx+b

Answer: y = -2x-1