- Đường thẳng [tex]d:ax=by=cz=t=>[/tex] [tex]d=\left\{\begin{matrix} x=\frac{1}{a} t& & \\ y=\frac{1}{b}t& & \\ z=\frac{1}{c}t& & \end{matrix}\right.[/tex][tex]=>\vec{u}=(\frac{1}{a};\frac{1}{b};\frac{1}{c})[/tex]
- Mặt phẳng [tex](P): \frac{x}{a}+\frac{y}{b}+\frac{z}{c}=1=>\vec{n}=(a;b;c)[/tex]
Có [tex]\vec{u}.\vec{n}=1+1+1=3\neq 0[/tex]
=> d cắt (P)