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`1+3+3^(2)+…….+3^(n-1) =((3^(n)-1))/(2)` |
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Answer» Let `P (n) :1+3+3^(2)+…..+3^(n-1)=(3^(n)-1)/(2)` `" If "n =1 , "the " L.H.S. =1` `R.H.S. =(3^(1)-1)/(2)=(3-1)/(2)=1` `:. " "L.H.S. =R.H.S.` Therefore the statement P (n) is true for n=1 Let P (n) be true for n=K. `:. P (k) : 1+3+3^(2) +.....+3^(k-1) =(3^(K)-1)/(2)` `P (k+1) :1+3+3^(2)+......+3^(k)` `=1+3+3^(2)+......+3^(k)` `=1+3+3^(2)+.......+3^(k-1)+3^(k)` `=(3^(k)-1)/(2) +3^(k)` `=(3^(k)-1+2.3^(k))/(2)=((1+2)3^(k)-1)/(2)` `=(3.3^(k)-1)/(2)=(3^(k+1)-1)/(2)` Then the statement P (n) is also true for n=K +1 , Hence form the principle of mathematical induction P (n) is true for `n in N` |
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