Question 10 of 25intermediate🔧 ApplyShort Answer4 marks

Find the equation of the line in vector and in cartesian form that passes through the point with position vector 2i^−j+4k^2\hat{i} - j + 4\hat{k} and is in the direction i^+2j^−k^\hat{i} + 2\hat{j} - \hat{k}.

Correct Answer

Let the position vector of the point be a⃗=2i^−j^+4k^\vec{a} = 2\hat{i} - \hat{j} + 4\hat{k} and the direction vector of the line be b⃗=i^+2j^−k^\vec{b} = \hat{i} + 2\hat{j} - \hat{k}.

The vector equation of the line passing through a point with position vector a⃗\vec{a} and parallel to vector b⃗\vec{b} is given by r⃗=a⃗+λb⃗\vec{r} = \vec{a} + \lambda \vec{b}. Substituting the given vectors, we get:

r⃗=(2i^−j^+4k^)+λ(i^+2j^−k^)\vec{r} = (2\hat{i} - \hat{j} + 4\hat{k}) + \lambda (\hat{i} + 2\hat{j} - \hat{k})

For the Cartesian form, the coordinates of the given point are (2,−1,4)(2, -1, 4) and the direction ratios are (1,2,−1)(1, 2, -1). Using the formula x−x1a=y−y1b=z−z1c\frac{x - x_1}{a} = \frac{y - y_1}{b} = \frac{z - z_1}{c}, we get:

x−21=y−(−1)2=z−4−1\frac{x - 2}{1} = \frac{y - (-1)}{2} = \frac{z - 4}{-1} x−21=y+12=z−4−1\frac{x - 2}{1} = \frac{y + 1}{2} = \frac{z - 4}{-1}
Exercise: EXERCISE 11.2 | Q: 5 | (Page Page 13)
For More Understanding

Explanation

The solution follows the standard derivation method shown in Example 6 of the provided context. The vector form is derived using the formula r⃗=a⃗+λb⃗\vec{r} = \vec{a} + \lambda \vec{b}, and the Cartesian form is obtained by equating the coefficients of i^,j^,k^\hat{i}, \hat{j}, \hat{k} and eliminating the parameter λ\lambda, resulting in the symmetric form x−x1a=y−y1b=z−z1c\frac{x - x_1}{a} = \frac{y - y_1}{b} = \frac{z - z_1}{c}.

Solution Steps

  1. Step 1: Identify the position vector a⃗=2i^−j^+4k^\vec{a} = 2\hat{i} - \hat{j} + 4\hat{k} and direction vector b⃗=i^+2j^−k^\vec{b} = \hat{i} + 2\hat{j} - \hat{k}.

  2. Step 2: Write the vector equation using r⃗=a⃗+λb⃗\vec{r} = \vec{a} + \lambda \vec{b}.

  3. Step 3: Identify the point coordinates (2,−1,4)(2, -1, 4) and direction ratios (1,2,−1)(1, 2, -1).

  4. Step 4: Write the Cartesian equation using x−x1a=y−y1b=z−z1c\frac{x - x_1}{a} = \frac{y - y_1}{b} = \frac{z - z_1}{c}.