Question

$\triangle abc$ and $\triangle def$ are similar. find the missing side length.
(the triangles are not drawn to scale.)
in $\triangle abc$: $ab=5$, $bc=8$, $ac=7$
in $\triangle def$: $ef=64$, $df=56$, $de=?$

Explanation:

Step1: Find similarity ratio

$\text{Ratio} = \frac{DF}{AC} = \frac{56}{7} = 8$

Step2: Calculate missing side

$\text{Side } DE = AB \times \text{Ratio} = 5 \times 8$

Answer:

40