Question

which choice is the explicit formula for the following geometric sequence 0.5,-0.1, 0.02, -0.004, 0.0008

Answer 1

Hello,

Answer is C

$a_1=0.5=\dfrac{1}{2} \\\\a_2=-0.1=-\dfrac{1}{10} =a_1*(-\dfrac{2}{10} )=a_1*(-\dfrac{1}{5} )\\\\a_3=0.02=\dfrac{2}{10^2} =a_2*(-\dfrac{2}{10} )=a_2*(-\dfrac{1}{5} )=a_1*(-\dfrac{1}{5} )^2\\...\\a_n=a_1*(-\dfrac{1}{5} )^{n-1}\\\\\boxed{a_n=0.5*(-0.2)^{n-1}}$