Question

12. Which term of the AP 75, 72, 69, ... is
first negative term ? If it is the nth term
find Sn.​

Answer 1

Answer:

-3 is the first negative term because in this series all terms are the multiple of 3 so 3 is also a term of this series and 3-3=0

0-3=-3

so a=-3

d=-3

and according to question nth term is also -3

so

$sn = \frac{n}{2} (2a + (n - 1)d) \\ = - 3(2( - 3) + ( - 3 - 1) - 3) \\ = - 3( - 6) + ( - 4) - 3) \\ = 18 + 12 \\ 30$.

hope it is right