Question

Given: AB || CD

Answer 1

First, find slope of point A and B using slope formula:
y2-y1 = 7-0 = -7
x2-x1    3-8     5

Next, use the point-slope formula to find the equation (pick either point A or B to substitute into this equation; the answer will be the same either way):
y-y1=m(x-x1)
y-7=-7(x-3)   (I used point B here)
        5
y=-7x +56 so the y-intercept is 56. Hurray! Part 1 down!
     5      5                                   5

Now to answer part 2. Since AB ll CD, they have the same slope: -7
                                                                                                         5
Therefore, you can use the handy point-slope equation to calculate the equation of line CD. (Remember you only need one of the points to use this equation if you already have the slope.) Since the only point given is D(5,5), we'll use that one:
y-y1=m(x-x1)
y-5=-7(x-5)
        5
y=-7x + 12 Yay! That's the answer to part 2; the equation of line CD
     5