Question

if SN the sum of first n terms of an ap is given by SN equals to 3n2 minus 4n then find nth term​

Answer 1

Step-by-step explanation:

$sn = 3 {n}^{2} - 4n \\ s(n - 1) = 3 {(n - 1)}^{2} - 4n + 4 \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 3 {n}^{2} + 3 - 6n - 4n + 4 \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 3 {n}^{2} - 10n + 7 \\ an = sn - s(n - 1) \\ an = 3 {n}^{2} - 4n - 3 {n}^{2} + 10n - 7 \\ an = 6n - 7$

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