Answer :

Let us assume the direction ratios of the line be r_{1}, r_{2}, r_{3}.

Then:

⇒ r_{1} = 2

⇒ r_{2} = –1

⇒ r_{3} = –2

Let us assume the direction cosines for the line be l, m, n

We know that for a line of direction ratios r_{1}, r_{2}, r_{3} and having direction cosines l, m, n has the following property.

⇒

⇒

⇒

Let us substitute the values of r_{1}, r_{2}, r_{3} to find the values of .

⇒

⇒

⇒

⇒

⇒

⇒

⇒

⇒

⇒

⇒

⇒

⇒

∴ The direction cosines for the given line is .

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