Question

In an A.P. given that the first term (a) = 54, the common difference
(d) = - 3 and the nth term (an) = 0, find n and the sum of first n terms (S.)
of the A.P.​

Answer 1

Answer:

$sn = \frac{n}{2 } (2a + (n - 1)d)$

$an = a + (n - 1)d$

0=54+(n-1)-3

-54/-3=n-1

18=n-1

n=18+1

n=19

sn=19/2(2x54+(19-1)-3

=19/2(108+18x-3)

=19/2(108-54)

=19/2x54

=27x19

=513

sn=513

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