3D Geometry 3 Question 45

####45. A line with positive direction cosines passes through the point P(2,1,2) and makes equal angles with the coordinate axes. The line meets the plane 2x+y+z=9 at point Q. The length of the line segment PQ equals

(2009)

(a) 1

(b) 2

(c) 3

(d) 2

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Answer:

Correct Answer: 45. (c)

Solution:

  1. Since,

l=m=n=13

Equations of line are x21/3=y+11/3=z21/3

x2=y+1=z2=r

[say]

Any point on the line is

Q(r+2,r1,r+2)

Q lies on the plane 2x+y+z=9

2(r+2)+(r1)+(r+2)=9

4r+5=9r=1

Q(3,0,3)

PQ=(32)2+(0+1)2+(32)2=3



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