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Joint Entrance Examination
Mathematics
3D Geometry
Question 439
Question 439 of 521
Medium
MCQ
If the angle
θ
\theta
θ
between the line
x
+
1
1
=
y
−
1
2
=
z
−
2
2
\dfrac{x+1}1=\dfrac{y-1}2=\dfrac{z-2}2
1
x
+
1
=
2
y
−
1
=
2
z
−
2
and the plane
2
x
−
y
+
λ
z
+
4
=
0
2x-y+\sqrt\lambda z+4=0
2
x
−
y
+
λ
z
+
4
=
0
is such that
sin
θ
=
1
3
\sin\theta=\dfrac13
sin
θ
=
3
1
, then the value of
λ
\lambda
λ
is
A
5
/
3
5/3
5/3
B
−
3
/
5
-3/5
−
3/5
C
3
/
4
3/4
3/4
D
−
4
/
3
-4/3
−
4/3
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Official solution
\[\sin\theta=\frac{|1(2)+2(-1)+2\sqrt\lambda|}{\sqrt{9}\sqrt{5+\lambda}}=\frac{2\sqrt\lambda}{3\sqrt{5+\lambda}}=\frac13\implies 4\lambda=5+\lambda\implies\lambda=\frac53.\]
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