Question

please solve it.a= -18.9 , d=2.5 , n=? ,an=3.6formulla:- an=a+(n-1)d

Answer 1

an = a+(n-1)d
3.6= -18.9+(n-1)2.5
3.6= -18.9+2.5n-2.5
3.6= -21.4 +2.5n
3.6+21.4 = 2.5n
25 = 2.5n
n = 25 / 2.5
n = 10