Question

Find the 13th term of the geometric sequence 3, -15, 75, ...​

Answer 1

Step-by-step explanation:

$an = a1 + (n - 1)d \\ d = a2 - a1 \\ a1 = 3 \\ a2 = - 15 \\ d = - 15 - 3 = - 18$

$a13 = 3 + (12) \times ( - 18) \\ a13 = 3 - 216 \\ a13 = - 213$

Answer 2

the terms of geometric sequence are 3, -15, 75

given,

1st term (a) = 3

second term (t2)=-15

common ratio (r) = t2/t1

=-15/3

=-5

then

t13= ar^n-1

=3×(-5)^13-1

=3×244140625

=3×244140625

=732421875.