What is the most number of regions that 9 lines can cut the plane into

Question

0 lines cuts the plane into at most 1 region.

A line cuts the plane into at most 2 regions.

2 lines cut the plane into at most 4 regions.

What is the most number of regions that 9 lines can cut the plane into?

Answer 1

Hint: Try to obtain the searched value by the induction.