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If lines x+55λ+2=4−2y10=1−3z−3\frac{x+5}{5\lambda+2} = \frac{4-2y}{10} = \frac{1-3z}{-3} and x−21=1+2y4λ=2+z3\frac{x-2}{1} = \frac{1+2y}{4\lambda} = \frac{2+z}{3} are perpendicular, than value of 'λ\lambda' is

Solution

✅ Correct Option: 2

We need to find the value of λ\lambda that makes the two given lines perpendicular to each other.


First, let's rewrite the lines in standard form so we can read off the direction ratios.

For Line 1: x+55λ+2=4−2y10=1−3z−3\dfrac{x+5}{5\lambda+2} = \dfrac{4-2y}{10} = \dfrac{1-3z}{-3}


The yy-part:


4−2y10=−(2y−4)10=y−2−5\dfrac{4 - 2y}{10} = \dfrac{-(2y - 4)}{10} = \dfrac{y - 2}{-5}


The zz-part:


1−3z−3=−(3z−1)−3=z−131\dfrac{1 - 3z}{-3} = \dfrac{-(3z - 1)}{-3} = \dfrac{z - \frac{1}{3}}{1}


So Line 1 becomes:


x+55λ+2=y−2−5=z−131\dfrac{x+5}{5\lambda+2} = \dfrac{y-2}{-5} = \dfrac{z - \frac{1}{3}}{1}


Direction ratios of Line 1: (5λ+2, −5, 1)(5\lambda + 2,\ -5,\ 1)


For Line 2: x−21=1+2y4λ=2+z3\dfrac{x-2}{1} = \dfrac{1+2y}{4\lambda} = \dfrac{2+z}{3}


The yy-part:


1+2y4λ=2(y+12)4λ=y+122λ\dfrac{1 + 2y}{4\lambda} = \dfrac{2(y + \frac{1}{2})}{4\lambda} = \dfrac{y + \frac{1}{2}}{2\lambda}


So Line 2 becomes:


x−21=y+122λ=z+23\dfrac{x-2}{1} = \dfrac{y + \frac{1}{2}}{2\lambda} = \dfrac{z+2}{3}


Direction ratios of Line 2: (1, 2λ, 3)(1,\ 2\lambda,\ 3)


Two lines are perpendicular when the dot product of their direction ratios equals zero:


a1a2+b1b2+c1c2=0a_1 a_2 + b_1 b_2 + c_1 c_2 = 0


Substituting:


(5λ+2)(1)+(−5)(2λ)+(1)(3)=0(5\lambda + 2)(1) + (-5)(2\lambda) + (1)(3) = 0


5λ+2−10λ+3=05\lambda + 2 - 10\lambda + 3 = 0


−5λ+5=0-5\lambda + 5 = 0


−5λ=−5-5\lambda = -5


λ=1\lambda = 1


Verification with λ=1\lambda = 1:

Line 1 direction ratios: (7, −5, 1)(7,\ -5,\ 1) and Line 2 direction ratios: (1, 2, 3)(1,\ 2,\ 3)


(7)(1)+(−5)(2)+(1)(3)=7−10+3=0(7)(1) + (-5)(2) + (1)(3) = 7 - 10 + 3 = 0 ✅


λ=1\boxed{\lambda = 1}

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