Answer & Step-by-step explanation:
These triangles are similar. This means that they are going to have the same ratios within their different sides.
AC and CE already have measurements so we are going to find the ratio between them. We can do this by dividing 21 by 7.
21 / 7 = 3
So, since the ratio between AC and CE is 3, then the rest of the triangle has a ratio of 3 with the other triangle.
So, let's set up an equation so we can find the value of x.
21/7 = (20 - x)/x
Cross multiply.
21x = 140 - 7x
Add 7x to both sides of the equation.
28x = 140
Divide 28 from 140.
x = 5
Now that we have the value of x, then we can find the measurement of CD.
The measurement of CD is 5.