Câu 37: \(x\cdot\frac37=\frac52\)
=>\(x=\frac52:\frac37=\frac52\cdot\frac73=\frac{35}{6}\)
=>Chọn B
Câu 38: \(\frac{1}{2\cdot4}+\frac{1}{4\cdot6}+\cdots+\frac{1}{\left(2x-2\right)\cdot2x}=\frac18\)
=>\(\frac{2}{2\cdot4}+\frac{2}{4\cdot6}+\cdots+\frac{2}{\left(2x-2\right)\cdot2x}=\frac14\)
=>\(\frac12-\frac14+\frac14-\frac16+\cdots+\frac{1}{2x-2}-\frac{1}{2x}=\frac14\)
=>\(\frac12-\frac{1}{2x}=\frac14\)
=>\(\frac{1}{2x}=\frac12-\frac14=\frac14\)
=>2x=4
=>x=2
=>Chọn D
Câu 40: Diện tích là: \(\frac12\cdot\frac{9}{10}\cdot\frac{5}{12}=\frac12\cdot\frac{5}{10}\cdot\frac{9}{12}=\frac12\cdot\frac12\cdot\frac34=\frac{3}{16}\left(\operatorname{cm}^2\right)\)
=>Chọn D
