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
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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
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