Question Details

Let  γ R be such that the lines  L 1 : x + 11 1 = y + 21 2 = z + 29 3 and  L 2 : x + 16 3 = y + 11 2 = z + 4 γ  intersect. Let 1R be the point of intersection of L1 and L2. Let O = ( 0 , 0 , 0 ) ,and n ^ denote a unit normal vector to the plane containing both the lines L1 and L2.

Match each entry in List-I to the correct entry in List-II.

List-I List-II
(P) γ equals
(1)  i ^ j ^ + k ^
(Q) A possible choice for  n ^ is (2)  3 2
(R)  O R 1 equals (3) 1
(S) A possible value of  O R 1 .   n ^ is (4)  1 6 i ^ 2 6 j ^ + 1 6 k ^

(5)  2 3

The correct option is

Options

A

(P) → (3)  (Q) → (4)  (R) → (1)  (S) → (2)

B

(P) → (5)  (Q) → (4)  (R) → (1)  (S) → (2)

C

(P) → (3)  (Q) → (4)  (R) → (1)  (S) → (5)

D

(P) → (3)  (Q) → (1)  (R) → (4)  (S) → (5)

Show Answer

Correct Answer :

Option C

(P) → (3)  (Q) → (4)  (R) → (1)  (S) → (5)

(P) → (3), (Q) → (4), (R) → (1), (S) → (5)

Solution :

The correct match is (P) → (3), (Q) → (4), (R) → (1), (S) → (5).

Step-by-step Derivation:

1. Finding the Point of Intersection and γ:
Let the symmetric equations of the lines L1 and L2 be equated to parameters λ and μ respectively:

L1:x+111=y+212=z+293=λ

L2:x+163=y+112=z+4γ=μ

Any general point on L1 can be expressed as:
(λ11,2λ21,3λ29)

Similarly, any general point on L2 can be expressed as:
(3μ16,2μ11,γμ4)

Since the lines intersect at a point R, their coordinates must be equal for some values of λ and μ:
From the x-coordinates:
λ11=3μ16λ3μ=5 --- (Equation 1)
From the y-coordinates:
2λ21=2μ112λ2μ=10λμ=5 --- (Equation 2)

Subtracting Equation 1 from Equation 2 gives:
2μ=10μ=5
Substituting μ=5 into Equation 2:
λ=10

Using these parameter values, the coordinates of the point of intersection R are:
x=1011=1
y=2(10)21=1
z=3(10)29=1
Thus, the position vector OR is:

OR=i^j^+k^

This matches entry (1) in List-II, meaning (R) → (1).

Now, equating the z-coordinates at the intersection point:
z=γμ41=5γ45γ=5γ=1
This matches entry (3) in List-II, meaning (P) → (3).

2. Finding the Unit Normal Vector n^:
The direction vector of line L1 is d1=i^+2j^+3k^.
The direction vector of line L2 (with γ=1) is d2=3i^+2j^+k^.
The normal to the plane containing both lines is parallel to the cross product of these two directions:

d1×d2=|i^j^k^123321|

=i^(26)j^(19)+k^(26)=4i^+8j^4k^

We can simplify the direction vector of the normal to i^2j^+k^.
The unit normal vector n^ is:

n^=±i^2j^+k^12+(2)2+12=±(16i^26j^+16k^)

This matches entry (4) in List-II, meaning (Q) → (4).

3. Calculating ORn^:
Using OR=i^j^+k^ and choosing the unit normal vector n^=16i^26j^+16k^:

ORn^=(1)(16)+(1)(26)+(1)(16)

=16+26+16=26=46=23

This matches entry (5) in List-II, meaning (S) → (5).

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