We know that the area of a semicircle = 1/2(πr^2)
r = the radius
We also know that the area of a rectangle = xy
x = width
y = length
In our problem,
r = w
x = w
y = w + 5
A(w) = w(w + 5) - 1/2(πw^2)
Let's simplify the right side of the function.
A(w) = w^2 + 5w - 1/2πw^2