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The sum of n terms of ap is n2-n Then the nth term will be

Prakruthi , 4 Years ago
Grade 10
anser 1 Answers
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Last Activity: 4 Years ago

Sn = 2n2 + 5n
Now choose n =1 and put in the above formula,
First term = 2+5 = 7
Now put n=2 to get the sum of first two terms = 2x4 + 5x 2= 8 + 10 = 18
This means  first term + second term = 18 but first term =7 as calculated above so,
second term = 18-7 = 11
common difference becomes, 11-7 = 4
AP becomes, 7, 11, 15, ....
nth term = a + (n - 1)d = 7 + (n-1)4 = 7 + 4n - 4 = 3 + 4n
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