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JEE Main 20262 AprilMorning Shift
Exam
JEE Main
Year
2026
Date
2 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Three Dimensional Geometry

JEE Main 2026 · 2 April · Morning Shift · Mathematics · Three Dimensional Geometry

Let a line L passing through the point (1, 1, 1) be perpendicular...

Let a line LL passing through the point (1,1,1)(1, 1, 1) be perpendicular to both the vectors 2i^+2j^+k^2\hat{i} + 2\hat{j} + \hat{k} and i^+2j^+2k^\hat{i} + 2\hat{j} + 2\hat{k}. If P(a,b,c)P(a, b, c) is the foot of perpendicular from the origin on the line LL, then the value of 34(a+b+c)34(a + b + c) is :

Options

  1. A5050
  2. B8080
  3. C100100
  4. D120120

Correct answer

C. 100100

Step-by-step solution

The direction vector of the line LL is given by the cross product of the two vectors to which it is perpendicular:

d⃗=(2i^+2j^+k^)×(i^+2j^+2k^)=2i^−3j^+2k^\vec{d} = (2\hat{i} + 2\hat{j} + \hat{k}) \times (\hat{i} + 2\hat{j} + 2\hat{k}) = 2\hat{i} - 3\hat{j} + 2\hat{k}

The equation of the line LL passing through (1,1,1)(1, 1, 1) is:

x−12=y−1−3=z−12=λ\dfrac{x - 1}{2} = \dfrac{y - 1}{-3} = \dfrac{z - 1}{2} = \lambda

Any point PP on the line LL has coordinates (2λ+1,−3λ+1,2λ+1)(2\lambda + 1, -3\lambda + 1, 2\lambda + 1).

Since P(a,b,c)P(a, b, c) is the foot of the perpendicular from the origin (0,0,0)(0, 0, 0) to the line LL, the vector OP→\overrightarrow{OP} is perpendicular to the direction vector d⃗\vec{d} of the line. Thus, their dot product is zero:

OP→⋅d⃗=0\overrightarrow{OP} \cdot \vec{d} = 0

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

4λ+2+9λ−3+4λ+2=04\lambda + 2 + 9\lambda - 3 + 4\lambda + 2 = 0

17λ+1=0⇒λ=−11717\lambda + 1 = 0 \Rightarrow \lambda = -\dfrac{1}{17}

Substituting λ=−117\lambda = -\dfrac{1}{17} into the coordinates of PP, we get:

a=2(−117)+1=1517a = 2\left(-\dfrac{1}{17}\right) + 1 = \dfrac{15}{17}

b=−3(−117)+1=2017b = -3\left(-\dfrac{1}{17}\right) + 1 = \dfrac{20}{17}

c=2(−117)+1=1517c = 2\left(-\dfrac{1}{17}\right) + 1 = \dfrac{15}{17}

The sum of the coordinates is:

a+b+c=1517+2017+1517=5017a + b + c = \dfrac{15}{17} + \dfrac{20}{17} + \dfrac{15}{17} = \dfrac{50}{17}

Therefore, the value of 34(a+b+c)34(a + b + c) is:

34×5017=10034 \times \dfrac{50}{17} = 100

Answer: 100100
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