Two sides of a triangle are 5 cm and 9 cm. Which must the third side $x$, in cm, satisfy?

Explanation

1. 01

   Each side is less than the sum of the other two: $x < 5 + 9 = 14$, and $9 < 5 + x$, so $x > 4$.

2. 02

   So $4 < x < 14$.