The feet of perpendicular from the point \(A(1,0,3)\) to the join of the points \(B(4,7,1)\) and \(C(3,5…

The feet of perpendicular from the point \(A(1,0,3)\) to the join of the points \(B(4,7,1)\) and \(C(3,5,3)\) is
  1. \(\left(\frac{5}{3}, \frac{7}{3}, \frac{17}{3}\right)\)
  2. \(\left(\frac{10}{3}, \frac{17}{3}, \frac{6}{3}\right)\)
  3. \(\left(0, \frac{1}{2}, \frac{3}{2}\right)\)
  4. \(\left(\frac{1}{5}, \frac{3}{5}, \frac{7}{5}\right)\)

Solution

Since equation of line joining points \(B(4,7,1)\) and \(C(3,5,3)\) is \(\begin{aligned} \frac{x-4}{4-3} & =\frac{y-7}{7-5}=\frac{z-1}{1-3} \\ \Rightarrow \quad \frac{x-4}{1} & =\frac{y-7}{2}=\frac{3-1}{-2}=\lambda \quad \text{(let)} ...(i) \end{aligned}\) Now the general point over the above line (i) is \(P(\lambda+4,2 \lambda+7,1-2 \lambda)\) Let point \(P\) is the foot of perpendicular of point \(A(1,0,3)\) over the line (i), so AP \(\perp\) line \(\begin{aligned} & \Rightarrow(\lambda+4-1)(1)+(2 \lambda+7-0)(2)+(1-2 \lambda-3)(-2)=0 \\ & \Rightarrow \lambda+3+4 \lambda+14+4 \lambda+4=0 \Rightarrow 9 \lambda+21=0 \\ & \Rightarrow \quad \lambda=-\frac{7}{3} \\ \end{aligned}\) \(\therefore\) The coordinate of point \(P\) is \(\left(4-\frac{7}{3}, 7-\frac{14}{3}, 1+\frac{14}{3}\right)=\left(\frac{5}{3}, \frac{7}{3}, \frac{17}{3}\right)\) Hence, option (a) is correct.

Asked in: AP EAMCET 2020 (21 Sep Shift 1)

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