Mình lỡ đánh nhầm 2 lần \(\frac{5}{14}\)nha :)) chỉ 1 lần thôi
\(\frac{x-199}{6}+\frac{x-199}{12}+\frac{x-199}{20}+\frac{x-199}{30}+\frac{x-199}{42}=\frac{5}{14}\)
\(\left(x-199\right)\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)=\frac{5}{14}\)
\(\left(x-199\right)\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)=\frac{5}{14}\)
\(\left(x-199\right)\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{6}-\frac{1}{7}=\frac{5}{14}\right)\)
\(\left(x-199\right)\left(\frac{1}{2}-\frac{1}{7}\right)=\frac{5}{14}\)
\(\left(x-199\right).\frac{5}{14}=\frac{5}{14}\)
\(\Leftrightarrow x-199=1\)
\(\Leftrightarrow x=200\)
\(\frac{x-199}{6}+\frac{x-199}{12}+\frac{x-199}{20}+\frac{x-199}{30}+\frac{x-199}{42}=\frac{5}{14}\)
\(\left(x-199\right).\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)=\frac{5}{14}\)
\(\left(x-199\right).\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)=\frac{5}{14}\)
\(\left(x-199\right).\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)=\frac{5}{14}\)
\(\left(x-199\right).\left(\frac{1}{2}-\frac{1}{7}\right)=\frac{5}{14}\)
\(\left(x-199\right).\left(\frac{7}{14}-\frac{2}{14}\right)=\frac{5}{14}\)
\(\left(x-199\right).\frac{5}{14}=\frac{5}{14}\)
\(x-199=\frac{5}{14}:\frac{5}{14}\)
\(x-199=1\)
\(x=1+199=200\)
(x-199).(1/2-1/3+1/3-1/4+...+1/6-1/7)
(x-199).(1/2-1/7)=5/14.5/14
(x-199).6/14=25/ 196
coøn laïi cau tu lam nhe cam on
