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JEE Main 202431 JanuaryEvening Shift
Exam
JEE Main
Year
2024
Date
31 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Determinants

JEE Main 2024 · 31 January · Evening Shift · Mathematics · Determinants

Let A be a 3 × 3 real matrix such that A( array ll 1 0 1 array ) =...

Let A be a 3×33 \times 3 real matrix such that A\left(101\begin{array}{ll}1 \\ 0 \\ 1\end{array}\right) = 2\left(101\begin{array}{ll}1 \\ 0 \\ 1\end{array}\right), A\left(−101\begin{array}{ll}- 1 \\ 0 \\ 1\end{array}\right) = 4\left(−101\begin{array}{ll}- 1 \\ 0 \\ 1\end{array}\right), A\left(010\begin{array}{ll}0 \\ 1 \\ 0\end{array}\right) = 2\left(010\begin{array}{ll}0 \\ 1 \\ 0\end{array}\right). Then, the system \left(A - 3I\right)\left(xyz\begin{array}{ll}x \\ y \\ z\end{array}\right) = \left(123\begin{array}{ll}1 \\ 2 \\ 3\end{array}\right)$ has

Options

  1. Aunique solution
  2. Bexactly two solutions
  3. Cno solution
  4. Dinfinitely many solutions

Correct answer

A. unique solution

Step-by-step solution

Let, A = \left[\begin{cases}{x}_{1} & {y}_{1} & {z}_{1} \\ {x}_{2} & {y}_{2} & {z}_{2} \\ {x}_{3} & {y}_{3} & {z}_{3}\end{cases}\right]

It is given that, A\left[101\begin{array}{ll}1 \\ 0 \\ 1\end{array}\right] = \left[202\begin{array}{ll}2 \\ 0 \\ 2\end{array}\right]

⇒ \left[x1+z1x2+z2x3+z3\begin{array}{ll}{x}_{1} + {z}_{1} \\ {x}_{2} + {z}_{2} \\ {x}_{3} + {z}_{3}\end{array}\right] = \left[202\begin{array}{ll}2 \\ 0 \\ 2\end{array}\right]

⇒x1+z1=2,x2+z2=0,x3+z3=0...(i)⇒ {x}_{1} + {z}_{1} = 2, {x}_{2} + {z}_{2} = 0, {x}_{3} + {z}_{3} = 0 . . . \left(i\right)

Also, A\left[−101\begin{array}{ll}- 1 \\ 0 \\ 1\end{array}\right] = \left[−404\begin{array}{ll}- 4 \\ 0 \\ 4\end{array}\right]

⇒ \left[−x1+z1−x2+z2−x3+z3\begin{array}{ll}- {x}_{1} + {z}_{1} \\ - {x}_{2} + {z}_{2} \\ - {x}_{3} + {z}_{3}\end{array}\right] = \left[−404\begin{array}{ll}- 4 \\ 0 \\ 4\end{array}\right]

⇒−x1+z1=−4,−x2+z2=0,−x3+z3=4...(ii)⇒ - {x}_{1} + {z}_{1} = - 4, - {x}_{2} + {z}_{2} = 0, - {x}_{3} + {z}_{3} = 4 . . . \left(ii\right)

Now, A\left[010\begin{array}{ll}0 \\ 1 \\ 0\end{array}\right] = \left[020\begin{array}{ll}0 \\ 2 \\ 0\end{array}\right]

⇒ \left[y1y2y3\begin{array}{ll}{y}_{1} \\ {y}_{2} \\ {y}_{3}\end{array}\right] = \left[020\begin{array}{ll}0 \\ 2 \\ 0\end{array}\right]

⇒y1=0,y2=2,y3=0...(iii)⇒ {y}_{1} = 0, {y}_{2} = 2, {y}_{3} = 0 . . . \left(iii\right)

Using \left(i\right)\text{and}\left(ii\right),</p><p>,</p><p>⇒ {x}_{1} = 3, {x}_{2} = 0, {x}_{3} = - 1</p><p></p><p>⇒ {z}_{1} = - 1, {z}_{2} = 0, {z}_{3} = 3</p><p></p><p>∴ A = \left[{30−1020−103\begin{cases}3 & 0 & - 1 \\ 0 & 2 & 0 \\ - 1 & 0 & 3\end{cases}\right]</p><p>Now, \left(A - 3I\right)\left[xyz\begin{array}{ll}x \\ y \\ z\end{array}\right] = \left[−123\begin{array}{ll}- 1 \\ 2 \\ 3\end{array}\right]

⇒ \left[\begin{cases}0 & 0 & - 1 \\ 0 & - 1 & 0 \\ - 1 & 0 & 0\end{cases}\right]\left[xyz\begin{array}{ll}x \\ y \\ z\end{array}\right] = \left[−123\begin{array}{ll}- 1 \\ 2 \\ 3\end{array}\right]

⇒ \left[−z−y−x\begin{array}{ll}- z \\ - y \\ - x\end{array}\right] = \left[123\begin{array}{ll}1 \\ 2 \\ 3\end{array}\right]

⇒z=−1,y=−2,x=−3⇒ z = - 1, y = - 2, x = - 3

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