Answer:
-18.703
Step-by-step explanation:
a₁=-28(-1/2)¹⁻¹
r=-1/2
a₁=-28
r=-1/2
S₉=a₁[tex]\frac{1-r^{9} }{1-r}[/tex]
S₉=-28[tex]\frac{1-(\frac{1}{2})^{9} }{1-(\frac{1}{2}) }[/tex]
S₉=[tex]-\frac{1197}{64}[/tex]
S₉=-18[tex]\frac{45}{64}[/tex] S₉=-18.703125
