Question

If AB is parallel to CD and the slope of CD is -8, what is the slope of AB

Answer 1

when the line is parallel, their gradients will be the same. Thus, since gradient of AB= gradient of CD, AB= -8.

Answer 2

To solve this question you need to know the definition of a parallel line. 
Parallel lines: two lines that have the same slope, but different y-intercepts.

Therefore, by definition AB HAS to have the same slope as CD. If it has a different slop, the lines cannot be parallel to each other. So, the answer is AB has a slope of -8. Hope this helped! Have a nice day! :)