To prove the equation 2 + 4 + 6 + ... + 2n = n(n + 1) for all positive integers using mathematical induction, we need to show that it holds for the base case (n = 1) and then demonstrate that if it holds for some arbitrary positive integer k, it also holds for k + 1.
**Step 1: Base Case**
Let's check the equation for the base case when n = 1:
2 = 1(1 + 1)
2 = 1(2)
2 = 2
The equation holds true for the base case.
**Step 2: Inductive Hypothesis**
Assume that the equation holds true for some arbitrary positive integer k, that is, assume that:
2 + 4 + 6 + ... + 2k = k(k + 1)
**Step 3: Inductive Step**
We need to show that if the equation holds for k, it also holds for k + 1.
We start with the left-hand side (LHS) of the equation:
2 + 4 + 6 + ... + 2k + 2(k + 1)
Using the assumption from the inductive hypothesis:
= k(k + 1) + 2(k + 1)
Factoring out (k + 1):
= (k + 1)(k + 2)
This matches the right-hand side (RHS) of the equation, which is n(n + 1) when n = k + 1:
= (k + 1)((k + 1) + 1)
= (k + 1)(k + 2)
Therefore, if the equation holds for k, it also holds for k + 1.
**Step 4: Conclusion**
By proving the base case and showing that if it holds for k, it also holds for k + 1, we have established that the equation 2 + 4 + 6 + ... + 2n = n(n + 1) is true for all positive integers by mathematical induction.