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Find sum1+4+10+20+35......n terms |
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Answer» Nth term of this series = an = n(n+1)(n+2)/6 = (1/6) *(cube(n)+ 3*sqr(n)+ 2n). Now sum of all n terms = sum of cubes of first n natural numbers + 3* ( sum of Squares of first n natural numbers + 2 ( sum of first n natural numbers).. Use standard identities of sum of first n natural numbers, sum of squares of first n natural numbers, sum of cubes of first n natural numbers.. you can find answer but you have to know n terms formula is n ( n +1)÷2 See the ques. Is wronge it is not a A.P. and not an G.P. |
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