Question

If the sum of first 6 terms of an AP is 12 and sum of 10 terms is60 then find the sum of n terms​

Answer 1

Answer:

S6 = 12

S10 = 60

sum of nth term is = n/2 (2a+(n-1)d)

Answer 2

Step-by-step explanation:

S6 = 12

n/2(2a+(n-1)d) = 12

6/2(2a+(6-1)d) = 12

2a + 5d = 4. .........(1)

S10 = 60

n/2(2a+(n-1)d) = 60

10/2(2a+(n-1)d) = 60

2a + 9d = 12. .........(2)

(1) - (2)

2a + 5d = 4

2a + 9d = 12

- - -

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4d = 8

d = 2

put d in (1)

2a + 10 = 4

a = -3

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

Substitute the values in the above equation and you'll get your answer....