CBSE Class 12 Maths 2010 Solved Paper

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Question : 16
Total: 29
Find the Cartesian equation of the plane passing through the points A (0, 0, 0) and B (3, -1, 2) and parallel to the line
x4
1
=
y+3
4
=
z1
7
Solution:  
Let the equation of plane be ax + by + cz + d = 0 …. (1)
Since the plane passes through the point A (0, 0, 0) and B(3, -1, 2), we have a × 0 + b × 0 + c × 0 + d = 0
⇒ d = 0 …. (2)
Similarly for point B (3, -1 , 2), a x 3 + b x (-1) + c x 2 + d = 0
3a – b + 2c = 0 (Using, d = 0) …(3)
Given equation of the line is
x4
1
=
y+3
4
=
z1
7

We can also write the above equation as
x4
1
=
y(3)
4
=
x(1)
7

The required plane is parallel to the above line.
Therefore, a × 1 + b × (-4) + c × 7= 0
⇒ a – 4b + 7c = 0 … (4)
Cross multiplying equations (3) and (4), we obtain:
a
(1)×7(4)×2
=
b
2×13×7
=
c
3×(4)1×(1)

a
7+8
=
b
221
=
c
12+1

a
1
=
b
19
=
c
11
= k
⇒ a = k , b = - 19k , c = - 11k
Substituting the values of a, b and c in equation (1), we obtain the equation of plane as:
kx - 19ky - 11kz + d = 0
⇒ k (x - 19y - 11z) = 0 (From equation(2))
⇒ x - 19y - 11z = 0
So, the equation of the required plane is x – 19y - 11z = 0
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