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[tex]s = 1 + 2 + ... +72 + 73[/tex]
[tex]s = 73 + 72 + ... + 2 + 1[/tex]
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[tex]2s = 74 + 74 + 74 + ... + 74[/tex]
[tex]2s = 73 \times 74[/tex]
[tex]s = \frac{73 \times 74}{2} \\ [/tex]
[tex]s = 73 \times 37 [/tex]
[tex]s = 2701[/tex]
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