Solution: The original formula can be a common factor, and the deformation is

y=x(ax？ +bx？ +c)-7

When x=-7, y=7.

-7(ax？ +bx？ +c)-7=7

Solution: ax? +bx？ +c=-2

The original formula is: y=-2x-7.

When x=7, substitute

y=-2×7-7=-2 1

I hope I can help you!