Question

question 3 of 10 what is the length of $overline{cd}$? in this diagram, $\triangle abcsim\triangle edc$.

Explanation:

Step1: Use similarity of triangles

Since $\triangle ABC\sim\triangle EDC$, we have $\frac{AC}{EC}=\frac{BC}{DC}$. So $\frac{21}{7}=\frac{20 - x}{x}$.

Step2: Cross - multiply

$21x = 7(20 - x)$.

Step3: Expand and solve

$21x=140 - 7x$, $28x = 140$, $x = 5$.

Answer:

B. 5