Prove what kind of number you get when you add 1 to the product of two consecutive odd numbers.

AlgebraNumber TheoryInteger PropertiesAlgebraic ManipulationProofConsecutive Odd NumbersPerfect Squares
2025/5/26

1. Problem Description

Prove what kind of number you get when you add 1 to the product of two consecutive odd numbers.

2. Solution Steps

Let 2n+12n+1 be an odd number, where nn is an integer. Then the next consecutive odd number is 2n+32n+3.
The product of these two consecutive odd numbers is (2n+1)(2n+3)(2n+1)(2n+3).
(2n+1)(2n+3)=4n2+6n+2n+3=4n2+8n+3(2n+1)(2n+3) = 4n^2 + 6n + 2n + 3 = 4n^2 + 8n + 3
Adding 1 to the product gives 4n2+8n+3+1=4n2+8n+44n^2 + 8n + 3 + 1 = 4n^2 + 8n + 4.
We can factor this expression as 4(n2+2n+1)4(n^2 + 2n + 1).
We can further factor the expression inside the parentheses: 4(n+1)2=[2(n+1)]24(n+1)^2 = [2(n+1)]^2.
Since nn is an integer, n+1n+1 is also an integer, and 2(n+1)2(n+1) is an even integer.
Therefore, [2(n+1)]2[2(n+1)]^2 is the square of an even integer. Since it is the square of 2(n+1)2(n+1), it is a perfect square.

3. Final Answer

Adding 1 to the product of two consecutive odd numbers results in the square of an even number (a perfect square).

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