Slope and Slope Intercept form?

Question

Okay so you have the two ordered pairs (3,8) and (9,0). What is the equation in slope intercept form and how did you get the y-intercept? I mean I know the slope is 8 over -6 I just don't get how to get the y-intercept.

Thanks!!

Answer 1

Put the line into point-slope form first and then rewrite it in slope-intercept form.  Point-slope form is:

y - y1 = m(x - x1)

where m is the slope and the line includes the point (x1, y1).  

You know that m = -8/6 = -4/3 and that the line includes the point (9,0) so the equation for the line is:

y - 0 = (-4/3)(x - 9)

y = (-4/3)(x - 9)

Distribute the (-4/3) and you will have the equation of the line in slope-intercept form.

y = (-4/3)x - (-4/3)9

y = (-4/3)x + 12

Then the y-intercept is 12.

Hope this helps you!