2. determine the sum of the first 400 odd numbers.

Odd numbers take the form , where is an integer. When , the last odd number would be 799. So we're adding

By reversing the order of terms, we have

and we can pair up terms in both sums at the same position to write

so that we are basically adding 400 copies of 800, and from there we can find the value of the sum right away:

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We could also make use of the formulas,

We have

it is contrapositive

i could not see the question too well so check yourself again too . this is because i want you to get it correct.

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step-by-step explanation:

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