BITSAT2013MathematicsThree Dimensional GeometryActual
Find the angle between the two planes 2 x + y -2 z =5 and 3 x-6 y-2 z=7
Options
- A⁻¹(4 / 21)
- B⁻¹(2 / 21)
- C⁻¹(1 / 21)
- D⁻¹(5 / 21)
Correct answer
A. ⁻¹(4 / 21)
Step-by-step solution
The angle between two planes is the angle between their normals. From the equation of the planes, the normal vectors are N ₁=2 i + j -2 k and N ₂=3 i -6 j -2 k Therefore, = | N ₁ N ₂ | N ₁ | | N ₂ | | = | (2 i + j -2 k ) (3 i -6 j -2 k ) 4+1+4 9+36+4 |= ( 4 21 ) Hence, = ⁻¹ ( 4 21 )