BITSAT 2019 Slot 2 Solved Paper

We have,
l+m+n=0 ........(i)
and l2=m2+n2 ........(ii)
Putting the value of l in Eq. (ii), we get
(m+n)2=m2+n2
⇒ m2+n2+2mn=m2+n2
⇒ mn=0
⇒ m=0,n=0
when m=0,l=−n
∴ Direction cosines are (−

1

√2

,0,

1

√2

).
When n=0,l=−m
∴ Direction cosines are (−

1

√2

,

1

√2

,0).
Angle between lines are
cos‌θ=(

−1

√2

×−

1

√2

)+(0×

1

√2

) +(

1

√2

×0)
cos‌θ=

1

2

,θ=π∕3