Answer:
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Explanation:
The two given triangles, triangle (BDE) and triangle (BAC) share the angle (<B) in common. Moreover, their bases, line (DE), and line (AC) are parallel, this means that through the corresponding angles postulate, angles (<BDE) and (<BAC) are congrunet. Moreover, angles (<BED) and (<BCA) are also congruent. Thus, triangles (BDE) and (BAC) are similar through angle-angle similarity.
The ratio between the corresponding sides of similar triangles is the same. Therefore, one can form the following equation,
.
Substitute,

Simplify,

Cross products,

Simplify, distribute, multiply every term inside the parenthesis by the term outside of it,

Inverse operations,
