Answer: a 1 /a 2 = b 1 /b 2 = c 1 /c 2.
- A a<sub>1</sub>a<sub>2</sub> + b<sub>1</sub>b<sub>2</sub> + c<sub>1</sub>c<sub>2</sub> = 0
- B a<sub>1</sub>/a<sub>2</sub> = b<sub>1</sub>/b<sub>2</sub> = c<sub>1</sub>/c<sub>2</sub>
- C a<sub>1</sub> = a<sub>2</sub>, b<sub>1</sub> = b<sub>2</sub>
- D a<sub>1</sub> + a<sub>2</sub> = 0
Correct answer: B. a<sub>1</sub>/a<sub>2</sub> = b<sub>1</sub>/b<sub>2</sub> = c<sub>1</sub>/c<sub>2</sub>
Explanation: Two lines are parallel if their direction ratios are proportional: a<sub>1</sub>/a<sub>2</sub> = b<sub>1</sub>/b<sub>2</sub> = c<sub>1</sub>/c<sub>2</sub>.
Three mutually perpendicular axes x, y, z meeting at the origin O, with a point P located by its (x, y, z) coordinates.
Concept context
Lines and planes in 3D space, direction cosines, distances, and angles