Question

Which of the term of the AP 21 ,18 ,15,.........is 0

Answer 1

GIVEN :–

• An A.P. series 21 , 18 , 15 , ...........

TO FIND :–

• Which term is "0" = ?

SOLUTION :–

• We know that nth term of A.P. is –

$\\ \large \bf \dag \: \: {\boxed{ \bf T_n = a + (n-1)d}}$

• Here –

$\\ \: \: \bf {\huge{.}} \: \: a = 21$

$\\ \: \: \bf {\huge{.}} \: \: d = - 3$

$\\ \: \: \bf {\huge{.}} \: \: T_n =0$

$\\ \: \: \bf {\huge{.}} \:\: n = ?$

• So that –

$\\ \bf \implies \bf 0 =21+ (n-1) (- 3 )$

$\\ \bf \implies \bf 0 =21 - 3n + 3$

$\\ \bf \implies \bf 3n =21 + 3$

$\\ \bf \implies \bf 3n =24$

$\\ \bf \implies \bf n = \cancel \dfrac{24}{3}$

$\\ \bf \implies \large{ \boxed{ \bf n =8}}$

▪︎ Hence , 8th term is "0" .