1 .Find formula the perimeter and area of a semicircle ?
2.Find formula the area of a circle whose circumference ?
Don't try to memorize too many formulas.
It is often very easy to "develop" your own by common sense and just translating the English into Math.
e.g. Isn't the perimeter of a semi-circle just the distance along the diameter plus the distance along the half circle
so Perimeter = 2r + (1/2)(2pi)(r)
= 2r + (pi)r
Your second sentence makes no sense, it is an incomplete statement.