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QJEEM22Ma4100: JEE Main 2022 Mathematics - Class 12 JEEM22Ma4100 Solution: If the length of the perpendicular drawn from the point , a on…

If the length of the perpendicular drawn from the point P(a,4,2)P(a, 4,2) , a >0 on the line x+12=y−33=z−1−1\frac{x+1}{2}=\frac{y-3}{3}=\frac{z-1}{-1} is 262 \sqrt{6} units and Q(α1,α2,α3)Q\left(\alpha_{1}, \alpha_{2}, \alpha_{3}\right) is the image of the point P in this line, then a+∑i=13αi\mathrm{a}+\sum\limits_{i=1}^{3} \alpha_{i} is equal to :

Multiple Choice Options

  • A 7
  • B 8
  • C 12
  • D 14

Step-by-Step Verified Solution

∵\because PR is perpendicular to given line, so

JEE Main 2022 (Online) 27th July Evening Shift Mathematics - 3D Geometry Question 140 English Explanation

2(2λ−1−a)+3(3λ−1)−1(−λ−1)=02(2\lambda - 1 - a) + 3(3\lambda - 1) - 1( - \lambda - 1) = 0

⇒a=7λ−2\Rightarrow a = 7\lambda - 2

Now,

∵\because PR=26PR = 2\sqrt 6

⇒(−5λ+1)2+(3λ−1)2+(λ+1)2=24\Rightarrow {( - 5\lambda + 1)^2} + {(3\lambda - 1)^2} + {(\lambda + 1)^2} = 24

⇒5λ2−2λ−3=0⇒λ=1\Rightarrow 5{\lambda ^2} - 2\lambda - 3 = 0 \Rightarrow \lambda = 1 or −35- {3 \over 5}

∵\because a > 0 so λ=1\lambda = 1 and a=5a = 5

Now ∑i=13αi=2\sum\limits_{i = 1}^3 {{\alpha _i} = 2} (Sum of co-ordinate of R) −- (Sum of coordinates of P)

=2(7)−11=3= 2(7) - 11 = 3

a+∑i=13αi=5+3=8a + \sum\limits_{i = 1}^3 {{\alpha _i} = 5 + 3 = 8}

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