The problem states that if $n$ is an odd integer, then $n^2 + 3n + 5$ is odd. We need to prove whether this statement is true or false.

Number TheoryNumber TheoryParityOdd and Even IntegersProof
2025/6/7

1. Problem Description

The problem states that if nn is an odd integer, then n2+3n+5n^2 + 3n + 5 is odd. We need to prove whether this statement is true or false.

2. Solution Steps

Since nn is an odd integer, we can write nn as n=2k+1n = 2k + 1, where kk is an integer.
Now, substitute n=2k+1n = 2k + 1 into the expression n2+3n+5n^2 + 3n + 5:
n2+3n+5=(2k+1)2+3(2k+1)+5n^2 + 3n + 5 = (2k + 1)^2 + 3(2k + 1) + 5
=(4k2+4k+1)+(6k+3)+5= (4k^2 + 4k + 1) + (6k + 3) + 5
=4k2+4k+1+6k+3+5= 4k^2 + 4k + 1 + 6k + 3 + 5
=4k2+10k+9= 4k^2 + 10k + 9
=4k2+10k+8+1= 4k^2 + 10k + 8 + 1
=2(2k2+5k+4)+1= 2(2k^2 + 5k + 4) + 1
Since 2k2+5k+42k^2 + 5k + 4 is an integer, let m=2k2+5k+4m = 2k^2 + 5k + 4. Then the expression becomes 2m+12m + 1, which is the form of an odd integer.
Therefore, if nn is an odd integer, then n2+3n+5n^2 + 3n + 5 is odd.

3. Final Answer

True

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