Câu 1: D
Câu 2: \(\dfrac{3\left(x-y\right)^2}{5}:\dfrac{10x-10y}{x+y}\)
\(=\dfrac{3\left(x-y\right)^2}{5}\cdot\dfrac{x+y}{10\left(x-y\right)}\)
\(=\dfrac{3}{50}\cdot\dfrac{\left(x-y\right)\left(x+y\right)}{1}=\dfrac{3\left(x^2-y^2\right)}{50}\)
=>Chọn C
Câu 3: C
Câu 4: B


