Question

If the sum of first 9 terms of an A.P is equal to sum of its first 11 terms, then what is the sum of its 20 terms?

Pls Anyone help me!!​

Answer 1

Answer: 0

Explanation:

Sum of the first 9 terms = 9/2 (2a + 8d)

Sum of the first 11 terms = 11/2 (2a + 10d)

S9 = S11

9a + 36d = 11a + 55d

2a = -19d

2a + 19d = 0...........(1)

S20 = 20/2 (2a + 19d)

= 20/2 (0) . .. ............from (1)

S20 = 0

Answer 2

Put the values into the formula....let me know if you need help....

Explanation: