1.

The distance of the point `(1,-5,""9)`from the plane `x-y+z=5`measured along the line `x=y=z`is :(1) `3sqrt(10)`(2) `10sqrt(3)`(3) `(10)/(sqrt(3))`(4) `(20)/3`A. `3sqrt(10)`B. `10sqrt(3)`C. `(10)/(sqrt(3))`D. `(20)/(3)`

Answer» Correct Answer - B
Equation of line passing through the point (1, -5, 9) and parallel to x=y=z is
`(x-1)/(1)=(y+5)/(1)=(z-9)/(1)=lambda" "("say")`
Thus, any point on this line is of the form `(lambda+1,lambda-5,lambda+9).`
Now, if `P(lambda+1,lambda-5,lambda+9)` is the point of intersection of line and plane, then
`(lambda+1)-(lambda-5)+lambda+9=5`
`implies" "lambda+15=5implieslambda=-10`
`:."Coordinates of point P are "(-9, -15, -1).`
Hence, required distance
`sqrt((1+9)^(2)+(-5+15)^(2)+(9+1)^(2))`
`=sqrt(10^(2)+10^(2)+10^(2))`
`=10sqrt(3)`


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