Question

find the sum of the first 25 terms of an A.P whose nth term is tn=2-3n

Answer 1

tn= 2-3(1)
t1=-1
t2=-4
t3=-7
...........
t25=-79

formula for
first number is a= -1
difference d=3
sn=n(n-1)/2
sn=-(25(-26))/2
sn=-25*-13
sn=-325