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TS EAMCET · Maths · Three Dimensional Geometry

The combined equation for a pair of planes is S2x2-6y2-12z2+18yz+2zx+xy=0. If one of the planes is parallel to
x+2y-2z=5, then the acute angle between the planes S=0 is

  1. A cos-11621
  2. B π2
  3. C 2π3
  4. D sin-1715
Verified Solution

Answer & Solution

Correct Answer

(A) cos-11621

Step-by-step Solution

Detailed explanation

S=2x2-6y2-12z2+18yz+2zx+xy=0 S=(x+2y-2z)(2x-3y+6z)=0 Hence, (x+2y-2z) is parallel to one plane. So, 1,2,-2, (2,-3,6) will be the required direction ratios. Here, cosθ=2-6-129×49=163×7=-1621 θ=cos-1-1621 {cos(-θ)=cosθ} θ=cos-11621