Question

Ap .21,18,15………an term -81

Answer 1

3*7=21,3*6=18,3*5=15,3*4=12 and contiously we can solve like this way

Answer 2

a=21
d=18-21=-3
tn=a+(n-1)d
-81=21+(n-1)(-3)
-81=21+-3n+3
-81=18-3n
-81-18=-3n
-99=3n
-99/-3=n
n=33
please mark as brain list