Question

Two lines with direction ratios \[(a_1,b_1,c_1)\] and \[(a_2,b_2,c_2)\] are parallel when:

Options

• \[a_1+a_2=b_1+b_2=c_1+c_2\]

• \[a_1a_2+b_1b_2+c_1c_2=0\]

• \[\frac{a_1}{a_2}=\frac{b_1}{b_2}=\frac{c_1}{c_2}\]

• \[a_1^2=a_2^2,\ b_1^2=b_2^2,\ c_1^2=c_2^2\]

Answer 1

Proportional direction ratios mean parallel lines. Thus, the corresponding direction ratios have one common ratio.