How do I find y-intercept given two points?

I realize this question has been asked many many times, but I can't seem to find the answer...





I have two points given and from them I must find the equation of the line in slope-intercept form.





The points are: (44.2, -22.8) and (25.2, 34.2).


I know how to find the slope (m). y2-y1/x2-x1


which would be...


(-22.8-34.2)/(44.2-25.2)


-57/9


m= -3





So far, the equation is y= -3x+b


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Now for the y intercept (b)...I get confused. I wouldn't say no to help finding the intercept but what I really want is just an equation to find the y-intercept.

How do I find y-intercept given two points?
just substitute either of the points in


b = 3x + y


either point should give the same answer (this is a good check)


using (x,y) = (44.2, -22.8)


then


b = 3(44.2) + (-22.8) = 109.8


so


y = -3x + 109.8





.....
Reply:Plug in the values (44.2,-22.8) into the equation y = -3x+b so that b is the only variable present. From there you can solve for the y - intercept ,which is b.





-22.8 = -3(44.2) + b


-22.8 = -132.6 + b


109.8= b
Reply:Use the point slope formula:





y - y1 = m(x - x1)


you can plug in either (-22.8, -34.2) or (44.2, -25.2) for x1 and y1





y -34.2 = -3(x - 25.2)


y - 34.2 = -3x + 25.2


y = -3x + 109.8





therefore in the form y = mx + b; b =109.8 which is the y intercept.