basic question

what is the angle between lines whose Dr's are given by

l+m+n=0
l2+m2-n2=0

i have read this same question 4 places but neither time could i understand what it means .Plz help...

6 Answers

62
Lokesh Verma ·

(l/k)2+(m/k)2+(n/k)2=1

where k2 is l2+m2+n2

thus, n/k2=1/2

n/k=±1/√2

now you can take it from here....

you should reduce l, m , n as l/k and m/k and n/k respectively.

1
Philip Calvert ·

itna toh maine bhi koshish ki thi par samajh mein hi nahi aaya ki do line kaha hai ??matlab [l m n] toh kisi ek hi line ke ho sakte hai na..

[7][7] toh angle kaise ...
i mean i couldn't understand what question means by two lines.. when [l m n] can belong to only one line in fact i didn;t understabd the quesition at all [2]

1
Philip Calvert ·

can anyone please post the complete soln...
or is if it is too lengthy plz explain the question..

11
Anirudh Narayanan ·

Bhaiya, are there pairs of straight lines in 3D geo as well? [2]

1
skygirl ·

l = -(n+m) --------1
put this one in the second eqn...

u will get .. 2m(m+n)=0 => m/n=0 or m/n= -1.

find l/n from 1.

now, u will get a ratio...

equalise it to some constant say.. k.

u have another eqn : l2+m2+n2=1.

put l,m,n in terms of k in this eqn.

find k..

hence find l,m,n.

u will get two values for each..

thence, find the angle in between : l1l2 + m1m2 +n1n2 = cosθ

1
Philip Calvert ·

okie bad question
Thanks [1]

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