We want to show that if we add two weird numbers, the sum is always an even number.

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Before we also write the actual proof, we must convince ourselves that the given statement has actually some truth to it. We deserve to test the statement through a few examples.

I prepared the table listed below to gather the results of few of the numbers that I offered to test the statement.


It shows up that the statement, the amount of 2 odd number is even, is true. However, by simply giving infinitely many examples carry out not constitute proof. The is difficult to list all feasible cases.

Instead, we need to display that the statement stop true for ALL possible cases. The only way to achieve that is to express an odd number in its basic form. Then, we include the 2 odd numbers composed in general kind to gain a sum of an even number to express in a general type as well.

To compose the evidence of this theorem, friend should already have a clear expertise of the general develops of both even and also odd numbers.

The number n is even if it deserve to be expressed as


where k is an integer.

On the various other hand, the number n is odd if it deserve to be composed as


such the k is some integer.



Note: The objective of brainstorming in composing proof is for us to know what the organize is trying to convey; and also gather enough information to connect the dots, which will certainly be offered to leg the hypothesis and also the conclusion.

Let’s take two arbitrary odd number 2a + 1 and 2b + 1 whereby a and also b space integers.

Since we room after the sum, we want to add 2a + 1 and 2b + 1.

left( 2a + 1 ight) + left( 2b + 1 ight)

which provides us

left( 2a + 1 ight) + left( 2b + 1 ight) = 2a + 2b + 2.

Notice that we can’t combine 2a and also 2b due to the fact that they room not similar terms. However, we are successful in combining the constants, hence 1 + 1 = 2.

What deserve to we perform next? If girlfriend think around it, there is a typical factor the 2 in 2a + 2b + 2. If we variable out the 2, we attain 2left( a + b + 1 ight).

What’s next? Well, if we look within the parenthesis, it’s obvious that what we have is just an integer. It may not appear as an creature at first because we watch a bunch of integers being included together.

Recall the Closure building of Addition for the collection of integers.

Suppose a and b belong come the collection of integers. The amount of a and b which is a+b is also an integer.

In fact, girlfriend can expand this closure residential property of enhancement to more than two integers. Because that example, the amount of the integers -7, -1, 0, 4, and also 10 is 6 i beg your pardon is additionally an integer. Thus,


Going ago to where we left off, in 2left( a + b + 1 ight), the expression inside the parenthesis is just an integer due to the fact that the amount of the integers a, b and 1 is just an additional integer. For simplicity’s sake, let’s speak to it essence k.

So then,


That way 2left( a + b + 1 ight) have the right to be to express as

2left( a + b + 1 ight) =2k

where 2k is the general form of an even number. It looks favor we have actually successfully completed what we desire to display that the amount of two odds is even.

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THEOREM: The amount of two odd numbers is an also number.

PROOF: intend 2a+1 and also 2b+1 are any type of two strange numbers wherein a and also b are integers. The amount of these two odd number is left( 2a + 1 ight) + left( 2b + 1 ight). This can be streamlined as 2a + 2b + 2 by combining comparable terms. Factor out the greatest common factor (GCF) of old2 native 2a+2b+2 to acquire 2left( a + b + 1 ight). Since the sum of integers is just an additional integer, speak integer k, climate k=a+b+1. By substitution, we have actually 2left( a + b + 1 ight) = 2k wherein 2k is plainly the general form of an also number. Therefore, the amount of 2 odd number is an also number. ◾️