D and E are the midpoints of AB and AC in a triangle with AB = 14 cm, AC = 18 cm and BC = 16 cm…

Step 1. The halves. $AD = DB = 14 \div 2 = 7$ cm and $AE = EC = 18 \div 2 = 9$ cm.

Step 2. The ratios. $\dfrac{AD}{DB} = \dfrac{7}{7} = 1$ and $\dfrac{AE}{EC} = \dfrac{9}{9} = 1$. They are equal.

Step 3. Decide. By the converse, $DE \parallel BC$. This is the midpoint theorem. The length of $BC$ is not needed.