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JEE Main 20179 AprilOnline
Exam
JEE Main
Year
2017
Date
9 April
Mode
Online
Subject
Mathematics
Chapter
Determinants

JEE Main 2017 · 9 April · Online · Mathematics · Determinants

If x = a, y = b, z = c is a solution of the system of linear...

If x=a,y=b,z=cx = a, y = b, z = c is a solution of the system of linear equations
x+8y+7z=0x + 8y + 7z = 0
9x+2y+3z=09x + 2y + 3z = 0
x+y+z=0x + y + z = 0
Such that the point (a,b,c)\left(a, b, c\right) lies on the plane x+2y+z=6x + 2y + z = 6 , then 2a+b+c2a + b + c equals:

Options

  1. A22
  2. B−1- 1
  3. C11
  4. D00

Correct answer

C. 11

Step-by-step solution

x+8y+7z=0...(i)9x+2y+3z=0...(ii)x+y+z=0...(iii)\begin{array}{ll}x + 8y + 7z = 0 . . . \left(i\right) \\ 9x + 2y + 3z = 0 . . . \left(ii\right) \\ x + y + z = 0 . . . \left(iii\right)\end{array}.....

Solve the equation \left(i\right) \text{ and } \left(iii\right)</p><p></p><p>⇒ 7y + 6z = 0</p><p>Solvetheequation(ii) and (iii)</p><p>Solve the equation \left(ii\right) \text{ and } \left(iii\right)

⇒7x+z=0⇒ 7x + z = 0

x=λ and ∣y=−6(−7λ)7∣ and z=−7λx = \lambda \text{ and } \left|y = \dfrac{- 6\left(- 7\lambda\right)}{7}\right| \text{ and } z = - 7\lambda

{x=λ and y=6λ and z=−7λ\begin{cases}x = \lambda & \text{ and } y = 6\lambda & \text{ and } z = - 7\lambda\end{cases}

⇒λ+12λ−7λ=6⇒6λ=6⇒λ=1\begin{array}{ll}⇒ \lambda + 12\lambda - 7\lambda = 6 \\ ⇒ 6\lambda = 6 \\ ⇒ \lambda = 1\end{array}|⇒2λ+6λ−7λ⇒λ=1\begin{array}{ll}⇒ 2\lambda + 6\lambda - 7\lambda \\ ⇒ \lambda = 1\end{array}<br/><br/>Hence,<br /><br />Hence,a = 1, b = 6, c = - 7<br/><br/><br /><br />∴ 2a + b + c = 1$

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