If f(x) = |x| and g(x) = |x| − 4, which transformation is applied to f(x) to get g(x)?

Use mathematical induction to prove the statement is true for all positive integers n, or show why it is false. 1^2 + 4^2 + 7^2 + + (3n - 2)^2 = [n(6n^2-3n-1)/2]