Question

If the sum of 1st 11 terms of an a.P is equal to sum of 1st 19 terms of that a.P then, find the sum of 1st 30 terms

Answer 1

Answer:

Step-by-step explanation:

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

Sum of 19 terms = (19/2)(a + a + 18d)

(11/2)(2a +10d) =(19/2)(2a+18d)

22a + 110d = 38a + 342d

-16a = 232d

-2a = 29d

2a +29d = 0

Sum of 30 terms = (30/2)(a + a + 29d)

15(2a + 29d)

= 15×0

= 0