the first term of an A. P. is 1 and the sum of first 15 terms is 225, find the common difference.
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Answer: 2
Step-by-step explanation:
a = 1 -------------- 1.
S15 = 225
=> 15/2 [2a + (15 - 1)d ] = 225
=> 2a + 14 d = 225 × 2 /15
=> 2(1) + 14 d = 30. (From 1.)
=> 14 d = 30 - 2
=> d = 28 / 14
=> d = 2
Hope it helps!!
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