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Three Dimensional Geometry

Question
CBSEENMA12033413

Find the equation of the plane which bisects the line joining the points (–1, 2, 3) and (3, – 5 6) at right angles.

Solution
Let A (– 1, 2, 3), B(3, –5, 6) be given points and C be mid-point of AB.

therefore space space space space space straight C space is space open parentheses fraction numerator negative 1 plus 3 over denominator 2 end fraction comma space fraction numerator 2 minus 5 over denominator 2 end fraction comma space fraction numerator 3 plus 6 over denominator 2 end fraction close parentheses
i.e. open parentheses 1 comma space minus 3 over 2 comma space 9 over 2 close parentheses
Since the plane passes through the point  open parentheses 1 comma space minus space 3 over 2 comma space 9 over 2 close parentheses
∴  equation of plane is
straight A left parenthesis straight x minus 1 right parenthesis space plus space straight B space open parentheses straight y plus 3 over 2 close parentheses space plus space straight C open parentheses straight z minus 9 over 2 close parentheses space equals space 0                         ...(1)
Direction ratios of AB are 3 + 1, –5 – 2, 6 – 3  i.e. 4, –7, 3.
∴ the line with direction ratios 4, –7, 3 is normal to the plane (1)
therefore space space space space 4 left parenthesis straight x minus 1 right parenthesis space minus space 7 space open parentheses straight y plus 3 over 2 close parentheses space plus space space 3 space open parentheses straight z minus 9 over 2 close parentheses space equals 0
therefore space space 4 straight x minus 4 minus 7 straight y minus 21 over 2 plus 3 straight z minus 27 over 2 space equals space 0
or space space space 4 straight x minus 7 straight y space plus space 3 straight z space minus space 28 space equals space 0
which is required equation of plane.

Some More Questions From Three Dimensional Geometry Chapter

Find the direction cosines of x, y and z-axis.