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JEE Main 202427 JanuaryMorning Shift
Exam
JEE Main
Year
2024
Date
27 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Matrices

JEE Main 2024 · 27 January · Morning Shift · Mathematics · Matrices

Let A = [ cases 2 & 0 & 1 1 & 1 & 0 1 & 0 & 1 cases ], B = [ cases...

Let A = \left[\begin{cases}2 & 0 & 1 \\ 1 & 1 & 0 \\ 1 & 0 & 1\end{cases}\right], B = \left[\begin{cases}{B}_{1} & {B}_{2} & {B}_{3}\end{cases}\right], where B1{B}_{1}, B2,B3{B}_{2}, {B}_{3} are column matrices, and {AB}_{1} = \left[100\begin{array}{ll}1 \\ 0 \\ 0\end{array}\right], {AB}_{2} = \left[230\begin{array}{ll}2 \\ 3 \\ 0\end{array}\right], {AB}_{3} = \left[321\begin{array}{ll}3 \\ 2 \\ 1\end{array}\right]
If α=∣B∣\alpha = | B | and β\beta is the sum of all the diagonal elements of BB, then α3+β3{\alpha}^{3} + {\beta}^{3} is equal to

Correct answer

0

Step-by-step solution

Given: A = \left[\begin{cases}2 & 0 & 1 \\ 1 & 1 & 0 \\ 1 & 0 & 1\end{cases}\right], B = \left[\begin{cases}{B}_{1} & {B}_{2} & {B}_{3}\end{cases}\right], {B}_{1} = \left[x1y1z1\begin{array}{ll}{x}_{1} \\ {y}_{1} \\ {z}_{1}\end{array}\right], {B}_{2} = \left[x2y2z2\begin{array}{ll}{x}_{2} \\ {y}_{2} \\ {z}_{2}\end{array}\right] and {B}_{3} = \left[x3y3z3\begin{array}{ll}{x}_{3} \\ {y}_{3} \\ {z}_{3}\end{array}\right].

⇒ {AB}_{1} = \left[\begin{cases}2 & 0 & 1 \\ 1 & 1 & 0 \\ 1 & 0 & 1\end{cases}\right]\left[x1y1z1\begin{array}{ll}{x}_{1} \\ {y}_{1} \\ {z}_{1}\end{array}\right] = \left[100\begin{array}{ll}1 \\ 0 \\ 0\end{array}\right]

⇒ \left[2x1+0+z1x1+y1+0x1+0+z1\begin{array}{ll}2{x}_{1} + 0 + {z}_{1} \\ {x}_{1} + {y}_{1} + 0 \\ {x}_{1} + 0 + {z}_{1}\end{array}\right] = \left[100\begin{array}{ll}1 \\ 0 \\ 0\end{array}\right]

⇒2x1+z1=1,x1+y1=0,x1+z1=0⇒ 2{x}_{1} + {z}_{1} = 1, {x}_{1} + {y}_{1} = 0, {x}_{1} + {z}_{1} = 0

⇒x1=1,y1=−1,z1=−1⇒ {x}_{1} = 1, {y}_{1} = - 1, {z}_{1} = - 1

⇒ {AB}_{2} = \left[\begin{cases}2 & 0 & 1 \\ 1 & 1 & 0 \\ 1 & 0 & 1\end{cases}\right]\left[x2y2z2\begin{array}{ll}{x}_{2} \\ {y}_{2} \\ {z}_{2}\end{array}\right] = \left[230\begin{array}{ll}2 \\ 3 \\ 0\end{array}\right]

⇒ {AB}_{2} = \left[2x2+z2x2+y2x2+z2\begin{array}{ll}2{x}_{2} + {z}_{2} \\ {x}_{2} + {y}_{2} \\ {x}_{2} + {z}_{2}\end{array}\right] = \left[230\begin{array}{ll}2 \\ 3 \\ 0\end{array}\right]

⇒2x2+z2=2,x2+y2=3,x2+z2=0⇒ 2{x}_{2} + {z}_{2} = 2, {x}_{2} + {y}_{2} = 3, {x}_{2} + {z}_{2} = 0

⇒x2=2,y2=1,z2=−2⇒ {x}_{2} = 2, {y}_{2} = 1, {z}_{2} = - 2

⇒ {AB}_{3} = \left[\begin{cases}2 & 0 & 1 \\ 1 & 1 & 0 \\ 1 & 0 & 1\end{cases}\right]\left[x3y3z3\begin{array}{ll}{x}_{3} \\ {y}_{3} \\ {z}_{3}\end{array}\right] = \left[321\begin{array}{ll}3 \\ 2 \\ 1\end{array}\right]

⇒ {AB}_{2} = \left[2x3+z3x3+y3x3+z3\begin{array}{ll}2{x}_{3} + {z}_{3} \\ {x}_{3} + {y}_{3} \\ {x}_{3} + {z}_{3}\end{array}\right] = \left[321\begin{array}{ll}3 \\ 2 \\ 1\end{array}\right]

⇒2x3+z3=3,x3+y3=2,x3+z3=1⇒ 2{x}_{3} + {z}_{3} = 3, {x}_{3} + {y}_{3} = 2, {x}_{3} + {z}_{3} = 1

⇒x3=2,y3=0,z3=−1⇒ {x}_{3} = 2, {y}_{3} = 0, {z}_{3} = - 1

⇒ B = \left[\begin{cases}1 & 2 & 2 \\ - 1 & 1 & 0 \\ - 1 & - 2 & - 1\end{cases}\right]

⇒α=∣B∣=3⇒ \alpha = | B | = 3

⇒β=1⇒ \beta = 1

⇒α3+β3=27+1=28⇒ {\alpha}^{3} + {\beta}^{3} = 27 + 1 = 28

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