a: \(=\dfrac{-4-2}{6}+\dfrac{4+2}{24}+\dfrac{4+2}{96}+\dfrac{2}{192}\)
\(=-1+\dfrac{1}{4}+\dfrac{1}{16}+\dfrac{1}{96}\)
\(=\dfrac{-96+24+6+1}{96}=\dfrac{-65}{96}\)
b: \(=\dfrac{-2+1}{4}+\dfrac{1}{8}+...+\dfrac{1}{256}\)
\(=\dfrac{-1}{4}+\dfrac{1}{8}+...+\dfrac{1}{256}\)
\(=\dfrac{-2+1}{8}+...+\dfrac{1}{256}=\dfrac{-1}{256}\)