Question

find the sum of 25th term of an AP which nth term is given by tn =(7-3n).

Answer 1

Fo finding first term,
First term = (7-3) = 4

For finding with term, we need to put n = 5.
So,
25th term = [7-3 (25)]
= ( 7-75)
= -67

Sum = Number of terms ÷ 2 × ( First term + Last term )
Sum = 25/2 × ( 4 -67)
Sum = 25/2 × (-63)
Sum = -1575 / 2

Hope it helps....