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Use the formula S ​=(n + 1)2 to find the sum of 1​ + 2​ + 3​ + ...​ + 780.

 

1​ + 2​ + 3​ + ...​ + 780 ​=

Guest Sep 21, 2017
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 #1
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[ 780 x 781] / 2 =304,590

Guest Sep 21, 2017
 #2
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Guests answer is correct but your formula is wrong

This is what it should be.

 

S=n(n+1) / 2

Melody  Sep 22, 2017

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