# How do you find the 5th term of a geometric sequence whose first term is 4 and whose common ratio is -2?

Jul 17, 2018

Two ways to arrive to result:

One way is calculate the 5th term applying definition of geometric sequence:

${a}_{1} = 4$
a_2=4·(-2)=-8
a_3=(-8)·(-2)=16
a_4=16·(-2)=-32
a_5=(-32)·(-2)=64

and so on

Other way is apply general term of a geometric sequence

a_n=a_1·r^(n-1)

For n=5, we have a_5=4·(-2)^4=64