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Distance of the point (2,4,−1)(2, 4, -1) from the line 10+2x2=y+34=6−z9\frac{10+2x}{2} = \frac{y+3}{4} = \frac{6-z}{9} is

Solution

✅ Correct Option: 3

The line is given as 10+2x2=y+34=6−z9\frac{10+2x}{2} = \frac{y+3}{4} = \frac{6-z}{9}

Simplifying:

10+2x2=2(5+x)2=5+x=x+51\frac{10+2x}{2} = \frac{2(5+x)}{2} = 5+x = \frac{x+5}{1}

6−z9=−(z−6)9=z−6−9\frac{6-z}{9} = \frac{-(z-6)}{9} = \frac{z-6}{-9}

The line can be written as:

x+51=y+34=z−6−9\frac{x+5}{1} = \frac{y+3}{4} = \frac{z-6}{-9}

A point on the line is A=(−5,−3,6)A = (-5, -3, 6) and the direction vector is b⃗=(1,4,−9)\vec{b} = (1, 4, -9)


The vector from point AA to point P(2,4,−1)P(2, 4, -1) is:

AP⃗=P−A\vec{AP} = P - A

AP⃗=(2,4,−1)−(−5,−3,6)\vec{AP} = (2, 4, -1) - (-5, -3, 6)

AP⃗=(7,7,−7)\vec{AP} = (7, 7, -7)


The cross product AP⃗×b⃗\vec{AP} \times \vec{b}:

AP⃗×b⃗=∣i⃗j⃗k⃗77−714−9∣\vec{AP} \times \vec{b} = \begin{vmatrix} \vec{i} & \vec{j} & \vec{k} \\ 7 & 7 & -7 \\ 1 & 4 & -9 \end{vmatrix}

i⃗\vec{i} component: 7(−9)−(−7)(4)=−63+28=−357(-9) - (-7)(4) = -63 + 28 = -35

j⃗\vec{j} component: −[7(−9)−(−7)(1)]=−(−63+7)=56-[7(-9) - (-7)(1)] = -(-63 + 7) = 56

k⃗\vec{k} component: 7(4)−7(1)=28−7=217(4) - 7(1) = 28 - 7 = 21

Therefore AP⃗×b⃗=(−35,56,21)\vec{AP} \times \vec{b} = (-35, 56, 21)


The magnitude of the cross product:

∣AP⃗×b⃗∣=(−35)2+562+212|\vec{AP} \times \vec{b}| = \sqrt{(-35)^2 + 56^2 + 21^2}

=1225+3136+441= \sqrt{1225 + 3136 + 441}

=4802= \sqrt{4802}

=2×492= \sqrt{2 \times 49^2}

=492= 49\sqrt{2}


The magnitude of the direction vector:

∣b⃗∣=12+42+(−9)2|\vec{b}| = \sqrt{1^2 + 4^2 + (-9)^2}

=1+16+81= \sqrt{1 + 16 + 81}

=98= \sqrt{98}

=72= 7\sqrt{2}


The distance from the point to the line:

d=∣AP⃗×b⃗∣∣b⃗∣d = \frac{|\vec{AP} \times \vec{b}|}{|\vec{b}|}

=49272= \frac{49\sqrt{2}}{7\sqrt{2}}

=7= 7

The distance is 77 units.

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