AP EAMCET Engineering 17 Sep 2020 Shift 1 Paper

Let l,m,n be the direction cosines of the required line.
Since, it is perpendicular to the lines whose direction cosines are proportional to 1,−2,−2 and 0,2,1 respectively
Thus, l−2m−2n=0 and 2m+n=0
On solving
‌

l

2

=‌

m

−1

=‌

n

2

Thus, DR's of required line are proportional to (2,−1,2)
Hence, direction cosines are =(‌

2

3

,−‌

1

3

,‌

2

3

)