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Gauss's Problem and Arithmetic Series

Remember the formula!

                             an = a1 + ( n - 1 )d ... d = 3

a50 = 1 + 49( 3 ) = 148

Plug it all in:

Sn = ( n / 2 )( a1 + an ) ... S50 = ( 50 / 2 )( a + 148 ) = 3725

It's a cinch if you know the formulas... and absolutely no fun if you don't!  Make flash cards!  Gauss's problem always helps me remember.  (That kid was scary!)
 

YOUR TURN:

Find the sum of the first 93 terms

-2 , 0 , 2 , 4 , 6 , 8 , 10 , ...

 

Findthe summation of ( 5 + 6k ) as k goes from 1 to 43
(You'll need to finda1andan. )