1-Write a function to calculate the area of a circle, given the radius. Notice that the formula is s=r^2, where s is the area and r is the radius. (In R, is represented as pi.)

2-Write a function to multiply each element of a vector by the average of the vector, given a vector.

3-Write a function to raise each element of a vector to its n-th power, given the vector and the n. Make the default of n to be 2.