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CBSE Class 10 Answered

if the sum of n terms of an AP is n squared plus 2 x . Find the AP and 20th term.
Asked by palani002001 | 08 Nov, 2015, 07:20: PM
answered-by-expert Expert Answer
The sum of n terms of an A.P. is n2+2n.
1st term a = 12 + 2 = 3
Sum up to 2nd term = 22 + 4 = 8
Hence, second term = 8 - 3 = 5
Hence, the common difference 'd' = 5 - 3 = 2
Hence, the A.P. starts with 3, and has a common difference of '2'.
The sequence can be written as 3, 5, 7, 9....
20th term = a + (20 - 1 )d = 3 + 19 X 2
= 3 + 38 = 41
Answered by satyajit samal | 09 Nov, 2015, 04:20: PM

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