Question

If a line has the direction ratio – 18, 12, – 4, then what are its direction cosine.

Options

• `(-9)/11, 6/11, (-2)/11`

• `(-11)/9, 11/6, (-11)/2`

• `11/9, 11/6, 11/2`

• None of these

Answer 1

`(-9)/11, 6/11, (-2)/11`

Explanation:

Direction ratio of a line are – 18, 12, – 4

Now `sqrt((-18)^6 + (12)^2 + (-4)^2) = sqrt(484)`

= `sqrt(2 xx 2 xx 11 xx 11)`

Direction cosine are `(-18)/22, 12/22, (-4)/22` or `(-9)/11, 6/11, (-2)/11`