the nth term of an AP is given by a_n= 4n - 5,then find the sum of first 25 terms of the AP.

if n=1

an= 4(1)-5 =-1

if n=2

an=4(2)-5 =3

therefore a= -1 ,a2= 3.... is the ap

d= 3-(-1) = 4

if n=25

an=4(25)-5 = 95

S25= n/2(a+an)

25/2(-1+95)

25/2(94) =25(47)=

1175

there fore th e sum of first 25 no og the ap will be 1175.

hope it helps

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