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The distance between the parallel planes 2x + y + 2z = 8 and 4x + 2y + 4z = 5 is
A11/4
B3/2
C11/12
D11/6
Answer & Solution
Correct answer: D. 11/6
1. Make the normals parallel and identical: divide the second by 2 to get 2x + y + 2z = 5/2.
2. Use d = |d₁ - d₂| / √(a² + b² + c²).
3. Numerator: |8 - 5/2| = 11/2.
4. Denominator: √(4+1+4) = 3. So d = (11/2)/3 = 11/6.
_Source: NCERT Class 12 Maths Part 2 Ch 11 "Three Dimensional Geometry", §11.9_
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