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Question
In an A.P. the first term is 25, nth term is –17 and the sum of n terms is 132. Find n and the common difference.
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Solution
First term a = 25
nth term = –17
`=>` Last term l = –17
Sum of n terms = 132
`=> n/2 [a + l] = 132`
`=>` n(25 – 17) = 264
`=>` n × 8 = 264
`=>` n = 33
Now, l = –17
`=>` a + (n – 1)d = –17
`=>` 25 + 32d = –17
`=>` 32d = – 42
`=> d = -42/32`
`=> d = -21/16`
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