Question

This belongs to Dc's and dr's
if the dc's of two lines are connected by relations l +m-n =0
6ln -12lm+ mn =0 then dc's of two line are.....?
(1/root14,2/root14,3/root14) , (1/root26,3/root26,4/root26)

Answer 1

The answer is option A

(1/root14,2/root14,3/root14)

Given below is the steps to solve this problem.

At first consider the fact that there are 3 unknowns and only 2 equations are given.

But we know the general property of direction cosines.

They are governed by the equation;

l²+m²+n²=1

Now we have 3 equations and 3 unknowns.

Now write l in terms of m and n, this will reduce the number of variables to two.

Substitute this in second equation.

Now you will get 2 equation and 2 unknowns.

Substitute this in third equation to get the final third degree equation.

Solving this will give the above mentioned result.

Thank you