3 years ago

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?

Mathematics

2 answers:

iVinArrow [24]3 years ago

5 0

Answer:

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

Step-by-step explanation:

Mamont248 [21]3 years ago

3 0

Answer: 0

Step-by-step 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

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