Question Details

Foot of perpendicular from origin on a line passing through (1,1,1) having direction ratios <2,3,4> ,is

Options

A

( 1129, 229, 729 )

B

( 1129, -229, -729 )

C

( 1129, 229, -729 )

D

( -1129, 229, -729 )

Show Answer

Correct Answer :

Option C

( 1129, 229, -729 )

Solution :

The correct option is:
( 1129, 229, -729 )

Step-by-Step Derivation:

Step 1: Write the equation of the line.
The equation of a line passing through a point (x1,y1,z1) with direction ratios <a,b,c> is given by:
x-x1 a = y-y1 b = z-z1 c

Substituting the given point (1,1,1) and direction ratios <2,3,4>, we get:
x-1 2 = y-1 3 = z-1 4 = λ

Step 2: Express a general point on the line.
Any general point P on this line can be written in terms of parameter λ as:
P = ( 2λ+1, 3λ+1, 4λ+1 )

Step 3: Relate the line to the origin.
Let P be the foot of the perpendicular from the origin O(0,0,0) to the line.
The direction ratios of the line segment OP are:
( 2λ+1-0, 3λ+1-0, 4λ+1-0 ) = ( 2λ+1, 3λ+1, 4λ+1 )

Step 4: Use the perpendicularity condition.
Since OP is perpendicular to the given line (which has direction ratios <2,3,4>), their dot product must be zero:
2(2λ+1) + 3(3λ+1) + 4(4λ+1) = 0

Step 5: Solve for λ.
Expanding and simplifying the equation:
4λ+2 + 9λ+3 + 16λ+4 = 0
29λ+9 = 0
λ = - 929

Step 6: Calculate coordinates of the foot of the perpendicular.
Substitute the value of λ back into the coordinates of point P:
For the x-coordinate:
x = 2 ( - 929 ) + 1 = - 1829 + 2929 = 1129
For the y-coordinate:
y = 3 ( - 929 ) + 1= - 2729 + 2929 = 229
For the z-coordinate:
z = 4 ( - 929 ) + 1= - 3629 + 2929 = - 729

Thus, the coordinates of the foot of the perpendicular from the origin onto the line are:
( 1129, 229, -729 )

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