! " !!#$ % &#& ' !(' ##' #))* +, , ' -- ' . /0-. 1 # ' + # ' 2#' 20#0' 2#' 23. 0. * . 0 1 + 2 + 3 + . . . + n-1 + n = Sn + n-1 + n-2 + . . . + 2 + 1 = S(n+1) + (n+1) + (n+1) + . . . + (n+1) + (n+1) = 2Sn (n+1) = 2S1 + 2 + 3 + . . . + n-1 + n = Sn + n-1 + n-2 + . . . + 2 + 1 = S(n+1) + (n+1) + (n+1) + . . . + (n+1) + (n+1) = 2Sn (n+1) = 2S 1 + 2 + 3 + . . . + n-1 + n = Sn + n-1 + n-2 + . . . + 2 + 1 = S(n+1) + (n+1) + (n+1) + . . . + (n+1) + (n+1) = 2Sn (n+1) = 2S 1 + 2 + 3 + . . . + n-1 + n = Sn + n-1 + n-2 + . . . + 2 + 1 = S(n+1) + (n+1) + (n+1) + . . . + (n+1) + (n+1) = 2Sn (n+1) = 2S 21)(n n S+=!###' + #) 4 . #3 13 13123131313131313133 ....+= ++++++++++ %- 2(2 #- ' 15 6 ' * 7 8 &1 )* * * +7 * 9 ' :9 ' # "9%* ' +1'
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