- Exam
- JEE Main
- Year
- 2021
- Date
- 17 March
- Shift
- Morning Shift
- Subject
- Mathematics
- Chapter
- Matrices
JEE Main 2021 · 17 March · Morning Shift · Mathematics · Matrices
If A = [ cases 2 & 3 0 & - 1 cases ], then the value of det ( A ^ 4...
Correct answer
0
Step-by-step solution
Given, A = \left[\begin{cases}2 & 3 \\ 0 & - 1\end{cases}\right]
⇒ {A}^{2} = \left[\begin{cases}2 & 3 \\ 0 & - 1\end{cases}\right]\left[\begin{cases}2 & 3 \\ 0 & - 1\end{cases}\right] = \left[\begin{cases}4 & 3 \\ 0 & 1\end{cases}\right]
⇒ {A}^{4} = \left[\begin{cases}4 & 3 \\ 0 & 1\end{cases}\right]\left[\begin{cases}4 & 3 \\ 0 & 1\end{cases}\right] = \left[\begin{cases}16 & 15 \\ 0 & 1\end{cases}\right]
⇒ {A}^{5} = \left[\begin{cases}16 & 15 \\ 0 & 1\end{cases}\right]\left[\begin{cases}2 & 3 \\ 0 & - 1\end{cases}\right] = \left[\begin{cases}32 & 33 \\ 0 & - 1\end{cases}\right]
⇒ {A}^{10} = \left[\begin{cases}32 & 33 \\ 0 & - 1\end{cases}\right]\left[\begin{cases}32 & 33 \\ 0 & - 1\end{cases}\right] = \left[\begin{cases}1024 & 1023 \\ 0 & 1\end{cases}\right] . . . . \left(i\right)
Now, 2A = \left[\begin{cases}4 & 6 \\ 0 & - 2\end{cases}\right]
⇒ Adj\left(2A\right) = {\left[\begin{cases}- 2 & 0 \\ - 6 & 4\end{cases}\right]}^{T}
⇒ Adj\left(2A\right) = \left[\begin{cases}- 2 & - 6 \\ 0 & 4\end{cases}\right]
⇒ {\left(Adj\left(2A\right)\right)}^{2} = \left[\begin{cases}- 2 & - 6 \\ 0 & 4\end{cases}\right]\left[\begin{cases}- 2 & - 6 \\ 0 & 4\end{cases}\right] = \left[\begin{cases}4 & - 12 \\ 0 & 16\end{cases}\right]
⇒ {\left(Adj\left(2A\right)\right)}^{4} = \left[\begin{cases}4 & - 12 \\ 0 & 16\end{cases}\right]\left[\begin{cases}4 & - 12 \\ 0 & 16\end{cases}\right] = \left[\begin{cases}16 & - 240 \\ 0 & 256\end{cases}\right]
⇒ {\left(Adj\left(2A\right)\right)}^{5} = \left[\begin{cases}16 & - 240 \\ 0 & 256\end{cases}\right]\left[\begin{cases}- 2 & - 6 \\ 0 & 4\end{cases}\right] = \left[\begin{cases}- 32 & - 1056 \\ 0 & 1024\end{cases}\right]
⇒ {\left(Adj\left(2A\right)\right)}^{10} = \left[\begin{cases}- 32 & - 1056 \\ 0 & 1024\end{cases}\right]\left[\begin{cases}- 32 & - 1056 \\ 0 & 1024\end{cases}\right] = \left[\begin{cases}1024 & - 1047552 \\ 0 & 1048576\end{cases}\right] . . . . . \left(ii\right)
From equation \left(i\right) \text{ and } \left(ii\right)⇒ {A}^{10} - {\left(Adj\left(2A\right)\right)}^{10} = \left[\right] - \left[\right] = \left[\right]⇒ det\left({A}^{10} - {\left(Adj\left(2A\right)\right)}^{10}\right) = \left|\right| = 0E = det \left({A}^{4}\right) + det \left({A}^{10} - ( Adj ( 2A ) {)}^{10}\right)⇒ E = {\left(det \left(A\right)\right)}^{4} + 0⇒ E = {\left(- 2 - 0\right)}^{4}⇒ E = 16$