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Three Dimensional Geometry

Question
CBSEENMA12033475

Find the distance between parallel planes:
2x  – y + 3z – 4 = 0 and 6x – 3y + 9z + 13 = 0.

Solution

The equations of given planes are
2x – y + 3 z – 4 = 0        ... (1)
and 6 x – 3 y + 9 z + 13 = 0        ....(2)
Let (x1, y1 , z1 ) be any point on plane (1)
∴ 2 x1 –y1 + 3 z1 – 4 = 0 or 2x1– y, + 3 z1 =4    . (3)
Length of perpendicular from (x1, y1 , z1 ) to the plane (2) is
 equals space fraction numerator open vertical bar 6 straight x subscript 1 minus 3 straight y subscript 1 plus 9 straight z subscript 1 plus 13 close vertical bar over denominator square root of left parenthesis 6 right parenthesis squared plus left parenthesis negative 3 right parenthesis squared plus left parenthesis 9 right parenthesis squared end root end fraction space equals space fraction numerator open vertical bar 3 space open parentheses 2 straight x subscript 1 space minus space straight y subscript 1 space plus space 3 space straight z subscript 1 close parentheses plus 13 close vertical bar over denominator square root of 36 plus 9 plus 81 end root end fraction space equals fraction numerator open vertical bar 3 space left parenthesis 4 right parenthesis space plus space 13 close vertical bar over denominator square root of 126 end fraction space equals fraction numerator 25 over denominator square root of 126 end fraction
which is required distance between the planes. 

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