Question

chứng minh rằng |x.y|=|x|.|y|

Answer 1

giả sử\(\left|x.y\right|=\left|x\right|.\left|y\right|\)

 \(\Leftrightarrow\left|x.y\right|:\left|x\right|=y\)

\(\Rightarrow\left|x\right|=\left|y\right|\)

\(\Rightarrow\left|xy\right|=\left|x\right|.\left|y\right|\)

suy ra điều phải chứng minh 

Answer 2

\(\left|x.y\right|=\left|x\right|.\left|y\right|\)

\(\Leftrightarrow\left|x.y\right|:\left|x\right|=\left|y\right|\)

\(\Leftrightarrow\left|y\right|=\left|y\right|\)

Vậy \(\left|x.y\right|=\left|x\right|.\left|y\right|\)