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Use the formula S = n (n + 1)2 to find the sum of 1  + 2  + 3  + ...  + 385.=

 

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Use the formula S = n2 to find the sum of 1  + 3 + 5  + ...  + 915. =

(Hint: To find  n, add 1 to the last term and divide by  2.)

 Sep 6, 2017
 #1
avatar+98005 
+2

 

 

Sum    1 + 2 + 3 + ....+  385    =     [ 385] [386] / 2  =   74305

 

Sum  of  first n odds  =  [ ( odd integer + 1 )  / 2 ] ^2  =  ( [ 915 + 1 ] .2 )^2  =

 

( 916 / 2)^2  =  458^2  = 209764 

 

 

cool cool cool

 Sep 6, 2017

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