Question

tìm x biết ( 1/2x4 + 1/4x6 + 1/6x8 ...+ 1/18x20) x 10 - \(x\) = 0

Answer 1

\(\left(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{18.20}\right).10-x=0\)

\(2\left(\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{18.20}\right).10-x=0\)

\(2\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{18}-\frac{1}{20}\right).10-x=0\)

\(2\left(\frac{1}{2}-\frac{1}{20}\right).10-x=0\)

\(2.\frac{9}{20}.10-x=0\)

\(9-x=0\)

\(x=9-0\)

\(x=9\)