2[1/2X4+1/4X6+1/6X8+...+1/Xx(X+2)]=11/45x2
2/2x4+2/4x6+2/6x8+....+2/Xx(X+2)=22/45
1/2-1/4+1/4-1/6+1/6-1/8+...+1/x-1/x+2=22/45
1/2-1/x+2=22/45
1/x+2=1/2-22/45
1/x+2=1/90
=>x+2=90
=>x=88
vậy x=88
\(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{x\left(x+2\right)}=\frac{11}{45}\)
\(\Rightarrow\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{x\left(x+2\right)}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+2}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{x+2}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{2}-\frac{22}{45}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{90}\)
=>x+2=90
=>x=90-2
=>x=88
vậy x=88