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| 1. |
Sn=3n×3n_4n find an |
| Answer» Sn=3n×3n - 4n=9n^2-4n----------------\xa0(1)putting n-1 in place of nSn-1=9(n-1)(n-1)-4(n-1)=9n^2-18n+9-4n+1Sn-1=9n^2-22n+10-------------------------(2)We know that\xa0Sum of n terms = sum of n-1\xa0terms + anSn=Sn-1 + anan=Sn-Sn-1Putting value of Sn and Sn-1an=9n^2-4n - (9n^2-22n+10)=9n^2-4n-9n^2+22n-10=18n-10Hence an=18n-10 | |