Q77 / 125 · BITSAT 2012 · Mathematics
Find the coordinates of the point where the line joining the points (2,-3,1) and (3,-4,-5) cuts the plane $2 x+y+z=7$
- A(1,2,-7)
- Correct answerB(1,-2,7)
- C(-1,-2,7)
- D(1,2,7)
Solution
The direction ratios of the line are $3-2,-4-(-3),-5-1$ i.e. 1,-1,-6
Hence equation of the line joining the given points is $\frac{x-2}{1}=\frac{y+3}{-1}=\frac{z-1}{-6}=r($ say $)$
Coordinates of any point on this line are $(r+2,-r-3,-6 r+1)$
If this point lies on the given plane $2 x+y+z=7$ then $2(r+2)+(-r-3)+(-6 r+1)=7 \Rightarrow r=-1$
Coordinates of any point on this line are $(-1+2,-(-1)-3,-6(-1)+1)$ i.e. (1,-2,7)
Hence, the correct answer is option: 'B'.