Since we know that x = a + b and f(x) = x^2, we can also say that f(x) = (a + b)^2.

By Theorem n, which was proved previously, we know that P(x) is true for all positive integers.

We have shown that P(x) is true for x = 1, 2, 3, 4; therefore we can deduce it is true for all other positive integers.

Since we know that P_1 is true, and that P_1 \rightarrow P_2, we can also say that P_2 is true.