9. A. She used y-values where she should have used x-values.

B. She did not keep the order of the points the same in the numerator and the denominator.

C. She mixed up the x- and y-values.

D. She should have added the values, not subtracted them.

B. She did not keep the order of the points the same in the numerator and the denominator.

Step-by-step explanation:

The formula to calculate slope is:

She instead used this formula:

The student made the mistake of not keeping the numerators and denominators in the same order.

answer: the resulting cross section is a rectangle. solution: a plane parallel to the base of a triangular prism will intersect a cross section that is the same shape as its bases. so the cross section is a triangle.

step-by-step explanation: