Suppose sn is defined as 2 + 22 + 23 + . . + 2n . what is the next step in your proof of sn = 2(2n - 1), after you verify that sn is valid for n = 1?
a. show that sn is valid for n = k + 2.
b. assume that sn is valid for n = k .
c. verify that sn is valid for n = 1.
d. show that sn is valid for n = k.