two sides of a triangle measure 4cm and 9cm

The third side of the triangle can have a range of lengths, as long as it is greater than the difference between the two given sides and less than the sum of the two given sides.

In this case, the possible range for the third side is:
9 - 4 < x < 9 + 4
5 < x < 13

Therefore, the third side can have a length between 5 cm and 13 cm.