Question Details

The distance of the point ( 7 , − 2 , 11 ) ( 7 , − 2 , 11 ) from the line  x 6 1 = y 4 0 = z 8 3  along the line  x 5 2 = y 1 3 = z 5 6 is :

Options

A

12

B

14

C

18

D

21

Show Answer

Correct Answer :

Option B

14

14

Solution :

The correct answer is 14.

To find the distance of the point P(7, -2, 11) from the line:
L1 : x6 1 = y4 0 = z8 3
measured along (or parallel to) the line:
L2 : x5 2 = y1 ��3 = z5 6
we will find the equation of a line passing through P(7, -2, 11) parallel to L2 and determine its intersection point with L1.

Step 1: Write the equation of the line passing through P and parallel to L2
The direction ratios of the line L2 are (2, -3, 6). Since the new line is parallel to L2, it shares the same direction ratios.
Therefore, the equation of the line passing through P(7, -2, 11) in parametric form is:
x7 2 = y+2 3 = z11 6 = λ

Any general point Q on this line can be written in terms of λ as:
Q = ( 2λ+7 , 3λ2 , 6λ+11 )

Step 2: Find the point of intersection of this line with L1
For Q to lie on the line L1, its coordinates must satisfy the equation of L1.
The equation of L1 is:
x6 1 = y4 0 = z8 3
Since the denominator of the y-term is 0, this implies that the y-coordinate is constant on this line:
y 4 = 0 y = 4

Substituting the y-coordinate of Q:
3λ2 = 4
3λ = 6
λ = 2

Now, substitute λ=2 back to find the coordinates of the intersection point Q:
x = 2(2)+7 = 3
y = 3(2)2 = 4
z = 6(2)+11 = 1
So, the intersection point is Q(3, 4, -1).

Let us verify if Q(3, 4, -1) lies on L1:
36 1 = 3
18 3 = 3
Since 3=3 and y = 4, Q lies on L1.

Step 3: Calculate the distance between P and Q
Using the distance formula:
d = (x2x1)2 + (y2y1)2 + (z2z1)2
Substitute the coordinates of P(7, -2, 11) and Q(3, 4, -1):
d = (37)2 + (4(2))2 + (111)2
d = (4)2 + 62 + (12)2
d = 16+36+144
d = 196
d = 14

The distance is 14.

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