Question

Find an explicit rule for the nth term of the sequence.

2, -8, 32, -128, ...

Answer 1

a1=2
a2=-8
a3=32
a4=-128

a2/a1=(-8)/2→a2/a1=-4
a3/a2=32/(-8)→a3/a2=-4
a4/a3=(-128)/32→a4/a3=-4

a2/a1=a3/a2=a4/a3=r=-4

an=a1*r^(n-1)
an=2*(-4)^(n-1)

The explicit rule for the nth term of the given sequence is an=2*(-4)^(n-1)