因式分解 $5xy-20y$。 答案 ... 使用集合表示法描述阴影区域。 答案 ... 在韦恩图中，阴影表示出代表 $A\cup B'$ 的区域。 答案

1. Identify and extract the common factor.

Both terms $5xy$ and $20y$ have a common factor of $5y$.

$5xy-20y=5y(x-4)$

1. Describe the shaded part of the Venn diagram in set notation.

The shaded region is inside $A$ but outside $B$.

Hence the region is
$A\cap B'.$

1. Identify the regions represented by $A\cup B'$.

$A\cup B'$ means the region in $A$ or in $B'$. So shade all of circle $A$ and all regions outside circle $B$. Equivalently, leave only the part in $B$ but not in $A$ unshaded.