Answer
(a) $P = 2r+\pi~r$
(b) $A = \frac{1}{2}~\pi~r^2$
Work Step by Step
(a) Since the radius is $r$, the diameter is $2r$
We can find the length $L$ of half the circumference:
$L = \frac{1}{2}~\pi~d$
$L = \frac{1}{2}~\pi~(2r)$
$L = \pi~r$
We can find the total perimeter of the region:
$P = 2r+\pi~r$
(b) We can find the area of half of the full circle:
$A = \frac{1}{2}~\pi~r^2$
