Question

Use the vector product to find the area of a triangle with vertices at the with coordinates (1,2,3) (4,-3,2) (8,1,1)

Answer 1

the cross product is the area of the parallelogram formed by two vectors.

The triangle has 1/2 that area.
So, which two vectors form the sides of the base?
If your points have vectors a,b,c then c-a and b-a will work just fine.
That is, figure 1/2 (3,-5,-1)x(7,-1,-2)