For each line, determine whether the slope is positive, negative, zero, or undefined.

Step 1 ：Determine the slope of a line given two points on the line. The slope is calculated by the change in y-values divided by the change in x-values, also known as rise over run.

Step 2 ：If the line is vertical, the slope is undefined.

Step 3 ：If the slope is positive, the line rises from left to right.

Step 4 ：If the slope is negative, the line falls from left to right.

Step 5 ：If the slope is zero, the line is horizontal.

Step 6 ：Use the function `determine_slope` to calculate the slope and check if it is positive, negative, zero, or undefined.

Step 7 ：\(\boxed{\text{The function `determine_slope` can be used to determine whether the slope of a line is positive, negative, zero, or undefined.}}\)