If the sum of the first four terms of an A.P. is 6 and the sum of its first six terms is 4, then the sum of its first twelve terms is

Question

Accepted Answer

Correct answer: A. (a) Sum of first 4 term S_4=6 42 (2a+3d )=6 ⇒2a+3d=3………… (1) Sum of first 6 terms S_6=4 62 (2a+5d )=4 ⇒2a+5d= 43……… (2) eq. (2) - eq. (1) (2a+5d )- (2a+3d )= 43-3 ⇒d=- 56 ∴2a+3(- 56)=3 ⇒a= 114 S_12= 122(2 114+ (12-1 )(- 56)) S_12=6(- 226)=-22

$If the sum of the first four terms of an A.P. is 6 and the sum of its first six terms is 4, then the sum of its first twelve terms is$

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