Step 1: Recall the relation between the areas of the similar triangles.

THEOREM: The ratio of the areas of two similar triangles is equal to the

ratio of the squares of their corresponding sides

\frac{Area \triangle ABC}{Area \triangle DEF} = (\frac{AB}{DE})^2 = (\frac{BC}{EF})^2 = (\frac{CA}{FD})^2

Step 2: Substitute all the known values in the theorem

EXAMPLE: \frac{Area \triangle ABC}{Area \triangle DEF} =(\frac{BC}{EF})^2

= \frac{64}{121} =(\frac{BC}{15.4})^2

Step 3: Simplify for the unknown value

EXAMPLE: (BC)^2 = \frac{64}{121} *(15.4)^2

BC = \sqrt{\frac{64}{121} *(15.4)^2)}

BC = \frac{8}{11} * 15.4

BC = \frac{123.2}{11}

BC = 11.2 cm