if the sum of nth term of an AP is given by sn =3² - 4 n then find the nth term (an) and sum of first 14th term
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Step-by-step explanation:
Sn = 3n^2 - 4n
Tn = Sn - Sn-1
= 3n^2 - 4n - { 3( n-1 )^2 - 4( n-1 ) }
= 3n^2 - 4n - 3n^2 + 6n - 3 + 4n - 4
Tn = 6n - 7
T(14) = 6(14) - 7
= 84 - 7
T(14) = 77
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