-->

Three Dimensional Geometry

Question
CBSEENMA12035858

Find the equation of the plane passing through the point (−1, − 1, 2) and perpendicular to each of the following planes: 2x + 3y – 3z = 2   and   5x – 4y + z = 6

Solution

The equation of the piane passing through the point  ( -1, -1, 2 ) is:

 

a( x + 1 ) + b( y + 1 ) + c ( z - 1 )= 0       ............(1)

 

where a, b and c are the direction ratios of the normal to the plane

.

It is given that the plane (1) is perpendicularto the planes.

 

2x + 3y - 3z = 2    and  5x - 4y + z = 6

 

 2a + 3b - 3c = 0                                 ..............(2)

 

5a - 4b + c = 0                                       ...............(3)

 

solving equations (2) and (3), we have:

a(3 x 1) - ( -4  x (-3) ) = b( -3 x 5) - (2 x 1) = c(2 x (-4) )- ( 3 x 5)a-9 = b-17 = c-23

So the direction ratios of the normal to the required plane are multiples of 9,

17, and 23.

 

Thus, the equation of the required plane is:

 

9(x + 1) + 17( y + 1) + 23( z - 2) = 0

 

or   9x + 17y + 23z = 20