InterviewSolution
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`1. 2 .3+2. 3 .4++n(n+1)(n+2)=(n(n+1)(n+2)(n+3))/4` |
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Answer» Let P (n) `: 1.2.3+2.3.4+3.4.5+……` `+n(n+1)(n+2)=1/4n(n+1)(n+2)(n+3)` For n=1, `L.H.S. =1.2.3=6` `R.H.S. =1/4 .1.(1+1)(1+2)(1+3)=6` `:. L.H.S. =R.H.S` `rArr` P (n) is true for n=1 Let P (n) be true for n=k `:. P (k) : 1.2.3 + 2.3.4+3.4.5+......` `.......+k(k=1)(k+2)` `=1/4 k(k+1)(k+2)(k+3)` For n=k+1 `P (k+1) : 1.2.3+2.3.4+3.4.5+........+k(k+1)` `(k+2)+(k+1)(k+2)(K+3)` `=1/4k(k+1)(k+2)(K+3)+(K+1)(K+2)(K+3)` `=(k+1)(K+2)(K+3) ((K)/(4)+1)` `=1/4 (k+1) (k+2) (k+3) (k+4)` `rArr` P (n) is also true for n=k+1 hence from the principle of mathematical induction P (n) is true for all natural numbers n. |
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