Alrighty, so, here's what's up:
Part A:
Write a proportion that can be used to find the length of side CD.
How I would do it:
You're given one side on the large triangle which measures 12.
The corresponding side on the smaller triangle measures 9.
Your proportion would be 9/12, this simplifies to 3/4.
This means that x (Side CD), when multiplied by 3/4 equals 12.
x*(3/4)=12
x=16
Part B:
What is the perimeter in units of triangle CDF?
The perimeter of a triangle is a+b+c, where a, b, and c are the sides of the triangle. We have sides a, and b already. a=12, b=16. Now we just need to find side c. You can find side c by using
the 3/4 proportion.
x*(3/4)=15
x=20
Side c=20
Now add up all of the sides: 12+16+20=48
The perimeter of the triangle is 48 units.
Hope this helps! (: