Answer:
undefined
The problem:
Find the slope for the line going through (3,4) and (3,-4).
Explanation:
Line up points vertically and subtract.
Then put 2nd difference over 1st.
( 3 , 4)
-(3 , -4)
------------
0 8
So the slope would have been 8/0 but this is undefined.
So the slope is undefined.
Also notice the x's are the same and the y's are difference so this is a vertical line. There is only rise in a vertical line and no run. Recall, slope is rise/run. You cannot divide by 0 so this is why we say the slope is undefined when the x's are always the same no matter the y.