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The vector equation of line passing through (2, -1, 3) and perpendicular to the lines

x23=y11=z+22\frac{x-2}{3} = \frac{y-1}{1} = \frac{z+2}{2} and x+34=y53=z+12\frac{x+3}{-4} = \frac{y-5}{-3} = \frac{z+1}{2} is

(Here λ\lambda is a parameter)

Solution

Correct Option: 1

The line must pass through (2,1,3)(2, -1, 3) and be perpendicular to the two given lines.

For the line x23=y11=z+22\frac{x-2}{3} = \frac{y-1}{1} = \frac{z+2}{2}, the direction vector is:

b1=3i^+1j^+2k^\vec{b_1} = 3\hat{i} + 1\hat{j} + 2\hat{k}

For the line x+34=y53=z+12\frac{x+3}{-4} = \frac{y-5}{-3} = \frac{z+1}{2}, the direction vector is:

b2=4i^3j^+2k^\vec{b_2} = -4\hat{i} - 3\hat{j} + 2\hat{k}


The direction vector of the required line is perpendicular to both given lines, so it can be found using the cross product:

b=b1×b2\vec{b} = \vec{b_1} \times \vec{b_2}

b=i^j^k^312432\vec{b} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 3 & 1 & 2 \\ -4 & -3 & 2 \end{vmatrix}

b=i^(122(3))j^(322(4))+k^(3(3)1(4))\vec{b} = \hat{i}(1 \cdot 2 - 2 \cdot (-3)) - \hat{j}(3 \cdot 2 - 2 \cdot (-4)) + \hat{k}(3 \cdot (-3) - 1 \cdot (-4))

b=i^(2+6)j^(6+8)+k^(9+4)\vec{b} = \hat{i}(2 + 6) - \hat{j}(6 + 8) + \hat{k}(-9 + 4)

b=8i^14j^5k^\vec{b} = 8\hat{i} - 14\hat{j} - 5\hat{k}


The vector equation of a line passing through a point with position vector a\vec{a} and having direction vector b\vec{b} is:

r=a+λb\vec{r} = \vec{a} + \lambda\vec{b}

The position vector of point (2,1,3)(2, -1, 3) is 2i^j^+3k^2\hat{i} - \hat{j} + 3\hat{k}

The direction vector is 8i^14j^5k^8\hat{i} - 14\hat{j} - 5\hat{k}

Therefore, the vector equation is:

r=(2i^j^+3k^)+λ(8i^14j^5k^)\vec{r} = (2\hat{i} - \hat{j} + 3\hat{k}) + \lambda(8\hat{i} - 14\hat{j} - 5\hat{k})

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