Create a proportion using the fact that the triangles are similar.
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Practice makes perfect
Let's take a look at the given picture. Notice that ∠ BCA and ∠ DCE are congruent as they are vertical angles.
Therefore, by the Angle-Angle Similarity Theorem, triangles ACB and ECD are similar. This means that corresponding sides of these triangles are proportional.
AB/ED=BC/DC
Now we will substitute the given side lengths and solve the proportion to find the length of AB.
