Question

find an equation for the nth term of the arithmetic sequence. -15, -6, 3, 12, ... select one: a. an = -15 9(n 1) b. an = -15 x 9(n - 1) c. an = -15 9(n 2) d. an = -15 9(n - 1)

Answer 1

$-15;-6;\ 3;\ 12;...\\\\a_n=a_1+(n-1)d\\\\a_1=-15;\ a_2=-6\\\\d=a_2-a_1\to d=-6-(-15)=-6+15=9\\\\a_n=-15+(n-1)\cdot9=\boxed{-15+9(n-1)}$