Question

9. In an A.P. if the 12th term is - 13 and the sum of its
first four terms is 24, find the sum of its first 10 terms.​

Answer 1

Answer:

the sum of first 10 terms will be zero

explanation

12 th term is -13 that means ,a + 11d = -13 equation ...1

sum of first four terms is 24 ,that mean

Sn = n/2 (2a + (n-1 )d)

24 = 4/2 (2a + (4-1)d)

24 = 2 (2a + 3d )

therefore , 2a +3d =12 equation...2

solving equation 1 and 2 you get d = -2

putting d = -2 in equation 1 ,you get a= 9 .

now sum of first 10 terms will be ,

Sn = n/2 (2a+(n-1 )d)

S10 = 10/2 (2×9 +(10-1)×(-2))

solving this you will get answer zero .