\(B=-\frac{1}{1.2}-\frac{1}{2.3}-\frac{1}{3.4}-...-\frac{1}{98.99}-\frac{1}{99.100}\\
=-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\right)\\
=-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\\
=-\left(1-\frac{1}{100}\right)=\frac{-99}{100}\)
<br class="Apple-interchange-newline"><div></div>B=−11.2 −12.3 −13.4 −...−198.99 −199.100 \\ =−(11.2 +12.3 +13.4 +...+198.99 +199.100 ) \\ =−(1−12 +12 −13 +13 −14 +...+198 −199 +199 −1100 ) \\ =−(1−1100 )=−99100
\(B=-\frac{1}{1.2}-\frac{1}{2.3}-\frac{1}{3.4}-...-\frac{1}{99.100}\)
\(B=\frac{-1}{1.2}+\frac{-1}{2.3}+\frac{-1}{3.4}+...+\frac{-1}{99.100}\)
\(B=-1-\frac{-1}{2}+\frac{-1}{2}-\frac{-1}{3}+\frac{-1}{3}-\frac{-1}{4}+...+\frac{-1}{99}-\frac{-1}{100}\)
\(B=-1-\frac{-1}{100}\)
\(B=-\frac{99}{100}\)