[tex]\colorbox{red}G\colorbox{blue}E\colorbox{pink}O\colorbox{green}M\colorbox{purple}E\colorbox{orange}T\colorbox{blue}R\colorbox{pink}I\colorbox{green}C[/tex]
[tex]\colorbox{purple}S\colorbox{orange}E\colorbox{red}R\colorbox{blue}I\colorbox{yellow}E\colorbox{green}S[/tex]
FORMULA:
[tex] s_{n} = \frac{ a_{1}( {r}^{n} - 1) }{r - 1} [/tex]
SOLUTION:
[tex] s_{11} = \frac{ \frac{1}{2} ( { - 1}^{11} - 1) }{ - 1 - 1} = \frac{ \frac{1}{2}( - 2) }{ - 2} = \frac{1}{2} [/tex]
ANSWER:
Therefore, the sum of the first 11 terms is
[tex]\huge\pink{\boxed{\frac{1}{2}}} [/tex]
