Question

\(B=\frac{3.4+2.9.16+3.12.20+4.15-24}{4.5+2.12.20+3.16.20+4.20.30}\)

\(C=\frac{9}{10}-\frac{1}{10.9}-\frac{1}{9.8}-.....-\frac{1}{3.2}-\frac{1}{2.1}\)

Dấu chấm là dấu x

Answer 1

\(C=\frac{9}{10}-\frac{1}{10.9}-\frac{1}{9.8}-...-\frac{1}{3.2}-\frac{1}{2.1}\)

\(C=\frac{9}{10}-\left(\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{9.8}+\frac{1}{9.10}\right)\)

\(C=\frac{9}{10}-\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

\(C=\frac{9}{10}-\left(\frac{1}{1}-\frac{1}{10}\right)\)

\(C=\frac{9}{10}-\frac{9}{10}=0\)