1 .Find formula the perimeter and area of a semicircle ?

2.Find formula the area of a circle whose circumference ?

1 answer

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.