The equation of the plane containing the line 2x-5y+z=3, x+y+4z=5 and parallel to the plane x+3y+6z=1 is
(1) x+3y+6z=-7
(2) x+3y+6z=7
(3) 2x+6y+12z=-13
(4) 2x+6y+12z=13
The equation of the plane containing the line 2x-5y+z=3, x+y+4z=5 and parallel to the plane x+3y+6z=1 is
(1) x+3y+6z=-7
(2) x+3y+6z=7
(3) 2x+6y+12z=-13
(4) 2x+6y+12z=13
If for a > 0, the feet of perpendiculars from the points A (a, -2a, 3) and B (0, 4, 5) on the plane lx + my + nz = 0 are points C (0, -a, -1) and D respectively, then the length of line segment CD is equal to:
(A) $\sqrt {41} $
(B) $\sqrt {31} $
(C) $\sqrt {66} $
(D) $\sqrt {55} $ Continue reading If for a > 0, the feet of perpendiculars from the points ….
Let P be a plane lx + my + nz = 0 containing the line, $\frac{{1 – x}}{1} = \frac{{y + 4}}{2} = \frac{{z + 2}}{3}$. If plane P divides the line segment AB joining points A (-3, -6, 1) and B (2, 4, -3) in ratio k : 1 then the value of k is equal to:
(A) 4
(B) 2
(C) 1.5
(D) 3 Continue reading Let P be a plane lx + my + nz = 0 containing the line ….
The distance of line $3y-2z-1=0=3x-z+4$ from the point $(2,-1,6)$ is:
(A) $2\sqrt 6$
(B) $\sqrt {26}$
(C) $2\sqrt 5 $
(D) $4\sqrt 2 $
Solution
We have, $3x-z+4=0$ or $z=3x+4$
& $3y-2z-1=0$ or $3y-2(3x+4)-1=0$ or $y=2x+3$
Any point $(x,y,z)$ on the line $ \equiv (t,2t + 3,3t + 4)$
Let $d$ be the distance between $(2,-1,6)$ & $ (t,2t + 3,3t + 4)$
Then, $d^2=(t-2)^2+(2t+3+1)^2+(3t+4-6)^2=14t^2+24$
Minimum $d$ = Required answer = $\sqrt {24}=2\sqrt 6$ when t = 0.
Answer: (A)
Let the acute angle bisector of the two planes $x-2y-2z+1=0$ and $2x-3y-6z+1=0$ be the plane P. Then which of the following points lies on P?
(A) $(0,2,-4)$
(B) $(4,0,-2)$
(C) $(-2,0,-\frac {1}{2})$
(D) $(3,1,-\frac {1}{2})$
Solution
Bisectors are given by,
$\frac{{x – 2y – 2z + 1}}{3} = \pm \frac{{2x – 3y – 6z + 1}}{7}$
$ \Rightarrow 7x – 14y – 14z + 7 = \pm (6x – 9y – 18z + 3)$
Hence, $x-5y+4z+4=0$ & $13x-23y-32z+10=0$
Let $\theta $ be the angle between $x-2y-2z+1=0$ & $x-5y+4z+4=0$
$\cos \theta = \frac{{|1 + 10 – 8|}}{{3 \times \sqrt {42} }} = \frac{1}{{\sqrt {42} }} < \frac{1}{{\sqrt 2 }}$
$\theta > 45^\circ $
So, $x-5y+4z+4=0$ is the obtuse angle bisector.
$\therefore $ Acute angle bisector $P \equiv 13x – 23y – 32z + 10 = 0$
The point $(-2,0,-\frac {1}{2})$ satisfies P.
Answer: (C)