You just need to plug those expressions inside the formula: it doesn't matter if they're expressions involving a variable instead of plain numbers: the formula becomes

If you want, you can simplify it by expanding the square and then multiply the two parenthesis:

Answer:2 and 5
Step-by-step explanation:
Since A is (-7,-4) and C is (7,3) for the x value from a to c is 14 for the y value from a to c is 7
Do 14 x 2/7 which is 4
Do 7 x 2/7 which is 2
then add (-7+4,-4+2) which is (-3,-2)