Explanation
D.C of the line are 1√3 , 1√3 , 1√3
Any point on the line at a distance t from P(2,−1,2) is (2+t√3,−1+t√3,2+t√3)
which lies on 2x+y+z=9.
⇒t=√3
Let →m1 and →m2 be vectors parallel to the two given lines.
Then, angle between the two given lines is same as the angle between →m1 and →m2.
→m1= Vector parallel to the line with direction ratios (1,1,2)=i+j+2k and
→m2= Vector parallel to the line with direction ratio ((√3−1),(−√3−1),4)=(√3−1)i+(−√3−1)j+4k
Let θ be the angle between the given lines.
Then cosθ=→m1.→m2|→m1||→m2|=(√3−1)−(√3+1)+8√1+1+4√(√3−1)2+(√3+1)2+16
⇒cosθ=6√6√24=12
⇒θ=π3
The given lines are parallel to the vector.
→b1=1+2j+2k and →b2=3i+2j+6k respectively.
So, the angle θ between them is given by
cosθ=→b1.→b2|→b1||→b1|=(i+2j+2k)(3i+2j+6k)|i+2j+2k||3i+2j+6k|
=3+4+12√1+4+4√9+4+36=1921
⇒θ=cos−1(1921)
(27,37,−67)
(37−27,67)
(23−13,23)
Since, the plane is perpendicular to the z axis, a=b=0
The plane passes through (2,-3,4).
So d=4c
a+b+cd=c4c=14
lf θ is the angle between two lines whose d.cs are l1,m1,n1 and l2,m2,n2, then
Σ(l1+l2)24cos2(θ2)+Σ(lI−l2)24sin2(θ2)=
Let →a1 and →a2 be unit vectors along the lines.
→a1=l1ˆi+m1ˆj+n1ˆk
→a2=l2ˆi+m2ˆj+n2ˆk
⇒l21+m21+n21=1 and l22+m22+n22=1
Consider the dot product of →a1 and →a2
→a1.→a2=(l1l2)+(m1m2)+(n1n2)
⇒cosθ=(l1l2)+(m1m2)+(n1n2)
S=Σ(l1+l2)24cos2(θ2)+Σ(lI−l2)24sin2(θ2)
⇒S=2+2(l1l2+m1m2+n1n2)4cos2θ2+2−2(l1l2+m1m2+n1n2)4sin2θ2
⇒S=2+2cosθ4cos2θ2+2−2cosθ4sin2θ2
Now, 1+cosθ=2cos2θ2 and 1−cosθ=2sin2θ2
⇒S=22+22
⇒S=2
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