Question

Find the sum of n terms of an A.P. whose nth terms is given by $a_n=5-6n$.

Answer 1

Given: tn = 5 - 6n
Put n=1, $t_1$= -1
n=2, $t_2$= -7
n=3, $t_3$= -13

Sum of n terms= n/2[2a+(n-1)d]
= n/2[2(-1)+(n-1)(-6)]
= n/2[-2-6n+6]
=n/2(4-6n)
=> n(2-3n)