S₉ = 255.5
Step-by-step explanation:
the sum to n terms of a geometric sequence is
[tex]S_{n}[/tex] = [tex]\frac{a_{1}(r^{n}-1) }{r-1}[/tex]
where a₁ is the first term and r the common ratio
here a₁ = 0.5 and r = [tex]\frac{a_{2} }{a_{1} }[/tex] = [tex]\frac{1}{0.5}[/tex] = 2 , then
S₉ = [tex]\frac{0.5(2^{9}-1) }{2-1}[/tex]
= [tex]\frac{0.5(512-1)}{1}[/tex]
= 0.5(511)
= 255.5