Cho đường thẳng \({d_1}:3x + 4y + 1 = 0\) và \({d_...

D

- Hướng dẫn giải

\(\begin{array}{l} \left\{ \begin{array}{l} {d_1}:3x + 4y + 1 = 0 \to {{\vec n}_1} = \left( {3;4} \right)\\ {d_2}:\left\{ \begin{array}{l} x = 15 + 12t\\ y = 1 + 5t \end{array} \right. \to {{\vec n}_2} = \left( {5; - 12} \right) \end{array} \right.\\ \Rightarrow \cos \varphi = \frac{{\left| {15 - 48} \right|}}{{\sqrt {9 + 16} .\sqrt {25 + 144} }} = \frac{{33}}{{65}}. \end{array}\)