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The no of terms in an AP is 40 and the last is -54,given that the sum of the 15 terms added to the sum of the first 30 terms is zero.calculate(1)the first term and common difference.(2)sum of progression

2 answers

a+39d = -54

S15 = 15/2 (2a+14d)
S30 = 30/2 (2a+29d)
So, 15/2 (2a+14d) + 30/2 (2a+29d) = 0
or, a+12d = 0

Now you have two equations, and you can find a and d, and then the sum S40.
Thanks we'll calculated
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