How many terms of the AP:24, 21, 18,… Must be taken so that their sum is 78? Question How many terms of the AP:24, 21, 18,… Must be taken so that their sum is 78? in progress 0 Math Raelynn 1 month 2021-08-19T07:42:14+00:00 2021-08-19T07:42:14+00:00 1 Answer 0 views 0

## Answers ( )

Step-by-step explanation:Sum of n-th term of an AP , Sn = (n/2) [ 2a + (n-1) d ]

Sn = 78 (given)

A/Q,

(n/2) [ 2 × 24 + ( n – 1 ) (-3) ] = 78

=> n [ 48 – 3n +3 ] = 78 × 2

=> n( 51 – 3n ) = 78 × 2

=> 3n( 17 – n) = 156

=> n( 17 – n) = 52

=>