We are asked to calculate f(4) by means of the following function:
f(n) = f(n - 1)² - 5
As you can see, in order to calculate f(n) first we have to specify the value of f(n - 1), we are given the value of f(1), so we can calculate the value of f(2), then f(3) and finally f(4), like this:
f(2) = f(2-1)² - 5 = f(1)² - 5 = 2² - 5 = 4 - 5 = -1
Then, f(2) = -1, now we can calculate f(3) like this:
f(3) = f(3 - 1)² - 5 = f(2)² - 5 = (-1)² - 5 = -4
Then f(3) = -4, now we can calculate f(4) like this:
f(4) = f(4 - 1)² - 5 = f(3)² - 5 = (-4)² - 5 = 16 - 5 = 11
Then, f(4) equals 11