Question

The sum of first 18 terms of an AP whose nth term is 3 − 2n is​

Answer 1

a=1

a2= -1

d= -1-1= -2

Sn= n/2[ 2a+(n-1)d]

= 18/2[2×1+ (18-1)×-2]

= 9[2+17×-2]

= 9[2-34]

= 9×-32

= -288