CBSE Class 12 Math 2013 Solved Paper

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Question : 21 of 29
 
Marks: +1, -0
Find the coordinates of the point, where the line x22 = y+14 = z22 intersects the plane x – y + z – 5 = 0. Also find the angle between the line and the plane.
OR
Find the vector equation of the plane which contains the line of intersection of the planes r.i^+2j^+3k^4 = 0 and r.2i^+j^k^+5 = 0 and which is perpendicular to the plane r.5i^+3j^6k^+8 = 0
Solution:
The equation of the given line is x22 = y+14 = z22 ... (1)
Any point on the given line is (3λ + 2, 4λ - 1 , 2λ + 2)
If this point lies on the given plane x – y + z – 5 = 0, then
3λ + 2 -(4λ - 1) + 2λ + 2 - 5 = 0
⇒ λ = 0
Putting λ = 0 in (3λ + 2, 4λ - 1 , 2λ + 2) , we get the point of intersection of the given line and the plane is (2, -1, 2).
Let θ be the angle between the given line and the plane
∴ sin θ = a.b|a||b| = (3i^+4j^+2k^).(i^j^+k^)32+42+2212+12+12 = 34+2293 = 187
⇒ θ = sin1(187)
Thus, the angle between the given line and the given plane is sin1(187)
OR
The equation of the given planes are
r.i^+2j^+3k^4 = 0 ... (1)
r.2i^+j^k^+5 = 0 ... (2)
The equation of the plane passing through the intersection of the planes (1) and (2) is
|r.i^+2j^+3k^4| + λ |r.2i^+j^k^+5| = 4 - 5λ ... (3)
Given that plane (3) is perpendicular to the plane r.5i^+3j^6k^+8 = 0
1 + 2λ × 5 + 2 + λ × 3 + 3 - λ × - 6 = 0
⇒ 19λ - 7 = 0
⇒ λ = 719
Putting λ = 719 in (3), we get
r|(1+1419)i^+(2+719)j^+(3719)k^|
= 4 - 3519
r.(3319i^+4519j^+5019k^) = 4119
r.33i^+45j^+50k^ = 41. This is the equation of the required plane.
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