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# Solution - If a line drawn from the point A( 1, 2, 1) is perpendicular to the line joining P(1, 4, 6) and Q(5, 4, 4) then find the co-ordinates of the foot of the perpendicular. - HSC Science (General) 12th Board Exam - Mathematics and Statistics

#### Question

If a line drawn from the point A( 1, 2, 1) is perpendicular to the line joining P(1, 4, 6) and Q(5, 4, 4) then find the co-ordinates of the foot of the perpendicular.

#### Solution

Let M be the foot of the perpendicular drawn from the point A (1, 2, 1) to the line joining P (1, 4, 6) and Q (5, 4, 4) .

Equation of a line passing through the points (x1,y1,z1) and (x2,y2,z2) is

(x-x_1)/(x_2-x_1) = (y-y_1)/(y_2-y_1)=(z-z_1)/(z_2-z1)

Equation of the required line passing through P (1, 4, 6) and Q( 5, 4, 4) is

(x-1)/4=(y-4)/0=(z-6)/-2=lambda

x=4lambda+1;y=4;z=-2lambda+6

∴ Coordinates of M are (4lambda+1,4,-2lambda+6)      ..........(1)

The direction ratios of AM are

4lambda+1-1,4-2,-2lambda+6-1

i.e 4lambda, 2,-2lambda+5

The direction ratios of given line are 4,0,-2.
Since AM is perpendicular to the given line

therefore 4(4lambda)+0(2)+(-2)(-2lambda+5)=0

therefore lambda=1/2

Putting  lambda=1/2 in (i) , the coordinates of M are (3,4,5 ).

Length of perpendicular from A on the given line

AM=sqrt((3-1)^2+(4-2)^2+(5-1)^2)=sqrt(24)units.

Is there an error in this question or solution?

#### APPEARS IN

2015-2016 (March) (with solutions)
Question 3.2.1 | 4 marks

#### Reference Material

Solution for question: If a line drawn from the point A( 1, 2, 1) is perpendicular to the line joining P(1, 4, 6) and Q(5, 4, 4) then find the co-ordinates of the foot of the perpendicular. concept: Equation of a Line in Space. For the courses HSC Science (General) , HSC Science (Electronics), HSC Science (Computer Science), HSC Arts
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