Mathematics · essential
Condition for parallel lines for JEE
Direction ratios and direction cosines and the angle between two intersecting lines
Formula
\(\frac{a_1}{a_2}=\frac{b_1}{b_2}=\frac{c_1}{c_2}\)
Variables: \((a_1,b_1,c_1)\), \((a_2,b_2,c_2)\) are direction ratios of the two lines.
Conditions: Ratios are interpreted where denominators are nonzero; equivalently the two triples are proportional.
Checking parallelism; identifying skew/non-skew cases.