Question

In an ap the sum of first n terms is 3nsquar plus thirteen n all division two plus two find the 25th term

Answer 1

Answer:25th term is 80

Step-by-step explanation:

n term sum = 3n²/2 + 13n/2

as we know that nth term= (Sum of nth term)-(sum of (n-1)th term)

METHOD 1

so 25th term = (sum of 25 terms) - ( sum of 24 terms)

=(3(25)²/2+(13×25)/2)-( 3(24)²/2+(13×24)/2)

= 1100 - 1020

= 80

METHOD 2

1st term = 8

sum of 2 terms = 19

2nd term = 19 - 8= 11

so. difference = 11- 8 = 3

25th term = (8 + (25 -1)×3) = 80

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