Find a recursive function rule for the sequence: -9, 18, -36, 72, -144

Question

A- f(1)=−9,  f(n)= −2f(n−1)

B- f(1)=−9,  f(n)= (−2)^(n) f(n)

C- f(1)=−9,  f(n)= −9(−2)^n

D- f(1)=−9,  f(n)= 2f(n−1)

please help!!!

Answer 1

Each number is -2 times the preceding number, so A.