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Consider the equation of the line r=i^+2k^+μ(4i^j^+2k^)\vec{r} = -\hat{i} + 2\hat{k} + \mu(4\hat{i} - \hat{j} + 2\hat{k}).

Match List-I with List-II

List-IList-II
(A) It passes through the point(I) 4, -1, 2
(B) Its direction ratios are(II) 421,121,221\frac{4}{\sqrt{21}}, \frac{-1}{\sqrt{21}}, \frac{2}{\sqrt{21}}
(C) Its Cartesian form is(III) (-1, 0, 2)
(D) Its direction cosines are(IV) x+14=y1=z22\frac{x+1}{4} = \frac{y}{-1} = \frac{z-2}{2}

Choose the correct answer from the options given below:

Solution

Correct Option: 4

The line is given as: r=i^+2k^+μ(4i^j^+2k^)\vec{r} = -\hat{i} + 2\hat{k} + \mu(4\hat{i} - \hat{j} + 2\hat{k})

This is in the vector form: r=a+μb\vec{r} = \vec{a} + \mu\vec{b}

Where:

a=i^+2k^\vec{a} = -\hat{i} + 2\hat{k} represents a point the line passes through

b=4i^j^+2k^\vec{b} = 4\hat{i} - \hat{j} + 2\hat{k} represents the direction of the line


(A) It passes through the point → (III) (-1, 0, 2)

From the position vector a=i^+2k^\vec{a} = -\hat{i} + 2\hat{k}:

Coefficient of i^\hat{i} = -1 → x-coordinate = -1

Coefficient of j^\hat{j} = 0 → y-coordinate = 0

Coefficient of k^\hat{k} = 2 → z-coordinate = 2

Point: (-1, 0, 2)


(B) Its direction ratios are → (I) 4, -1, 2

From b=4i^j^+2k^\vec{b} = 4\hat{i} - \hat{j} + 2\hat{k}:

Coefficient of i^\hat{i} = 4

Coefficient of j^\hat{j} = -1

Coefficient of k^\hat{k} = 2

Direction ratios: 4, -1, 2


(C) Its Cartesian form is → (IV) x+14=y1=z22\frac{x+1}{4} = \frac{y}{-1} = \frac{z-2}{2}

The Cartesian form is: xx1a=yy1b=zz1c\frac{x - x_1}{a} = \frac{y - y_1}{b} = \frac{z - z_1}{c}

Where (x1,y1,z1)(x_1, y_1, z_1) = (-1, 0, 2) and (a,b,c)(a, b, c) = (4, -1, 2)

x(1)4=y01=z22\frac{x - (-1)}{4} = \frac{y - 0}{-1} = \frac{z - 2}{2}

x+14=y1=z22\frac{x + 1}{4} = \frac{y}{-1} = \frac{z - 2}{2}


(D) Its direction cosines are → (II) 421,121,221\frac{4}{\sqrt{21}}, \frac{-1}{\sqrt{21}}, \frac{2}{\sqrt{21}}

Direction cosines are obtained by dividing each direction ratio by a2+b2+c2\sqrt{a^2 + b^2 + c^2}

Magnitude:

42+(1)2+22\sqrt{4^2 + (-1)^2 + 2^2}

=16+1+4= \sqrt{16 + 1 + 4}

=21= \sqrt{21}

Direction cosines: 421,121,221\frac{4}{\sqrt{21}}, \frac{-1}{\sqrt{21}}, \frac{2}{\sqrt{21}}


Final matching:

(A) → (III) (-1, 0, 2)

(B) → (I) 4, -1, 2

(C) → (IV) x+14=y1=z22\frac{x+1}{4} = \frac{y}{-1} = \frac{z-2}{2}

(D) → (II) 421,121,221\frac{4}{\sqrt{21}}, \frac{-1}{\sqrt{21}}, \frac{2}{\sqrt{21}}

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