Question

the first term of an A.P. is 1 and the sum of first 15 terms is 225 ,find the common difference.

Answer 1

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Answer 2

Answer:

First term of an AP is 1

so, a=1

and, Sum of 15 terms = 225

S15 = 225

15/2(2a+ (15-1)d)= 225

15/2(2+14d)=225

2+(14)d = 30

14d= 28

d= 2

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