First, we expand the equation:

Then, we combine certain terms in order to simplify them using trigonometry identities.

Note these identities:
Pythagoran relation:

Sum and Difference Formula/Identities:

Thus, if we apply these identities, the simplified equation would be:

Simplying further, the answer would be
The answer is 3.925 i believe that is the answer
B. The fraction 4/9 is 4 times as large as 1/9
You can calculate the arc lenght by using this formula:
arc length = 2π*r*(A/360) , where A=angle of the arc.
So for you it would be:
arc length = 2π*4*(72/360) = 5.03
I hope that helped.