the sum of first n terms of ap is 2n square+ 5n then its nth term is?
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4n+3
Step-by-step explanation:
Sn = 2n²+5n
S1 = 2 (1)² + 5(1) = 2(1)+ 5 = 2+5 =7
S2 = 2 (2)² + 5(2) = 2(4)+ 10 = 8 + 10 = 18
S3 = 2 (3)² + 5(3) = 2(9)+ 15 = 18 + 15 = 33
a1 = S1 = 7
a2 = S2 - S1 = 18 -7 =11
a3 = S3 - S2 = 33 - 18 = 15
AP is 7 , 11 ,15 ,....
a = 7
d = 11-7 =4
an = a + (n-1) d
an = 7 + (n-1) 4
= 7 + 4n - 4
= 4n +3
Hope the solution is clear...
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