SIFAT-SIFAT DETERMINAN MATRIKS
Misalkan A dan B adalah matriks berukuran \(n \times n\) dan bukan matriks singular. Matriks singular adalah matriks yang determinannya sama dengan nol. (1) \(\color{blue} |\textbf{A}^{\text{T}}| = |\textbf{A}|\) (2) \(\color{blue} |k\cdot \textbf{A}| = k^n \cdot |\textbf{A}|\) (3) \(\color{blue} |\textbf{A}\cdot \textbf{B}| = |\textbf{A}| \cdot |\textbf{B}| \) (4) \(\color{blue} |\textbf{A}^{-1}| = \dfrac{1}{|\textbf{A}|}\)CONTOH SOAL
Soal 1 Diketahui \(\textbf{A} = \begin{bmatrix}2 & -3\\2 & 1 \end{bmatrix}\). Tentukan \(|\textbf{A}^{\text{T}}|\)
\(|\textbf{A}| = 2(1)\:-\:(-3)(2)\)
\(|\textbf{A}| = 2 + 6 = 8\)
\(|\textbf{A}^{\text{T}}| = |\textbf{A}|\)
\(|\textbf{A}^{\text{T}}| = 8\)
Soal 2
Diketahui \(\textbf{B} = 3\cdot\begin{bmatrix}1 &-1\\3 & 2 \end{bmatrix}\). Tentukan \(|\textbf{A}|\)
Matriks B berukuran 2 × 2, sehingga:
\(|\textbf{B}| = 3^{\color{blue}2} \cdot \begin{vmatrix}1 &-1\\3 & 2 \end{vmatrix}\)
\(|\textbf{B}| = 9 \cdot (1(2) \:-\:(-1)(3))\)
\(|\textbf{B}| = 9 \cdot (2 + 3)\)
\(|\textbf{B}| = 9 \cdot 5\)
\(|\textbf{B}| = 45\)
Soal 3
Diketahui \(\textbf{C} = \begin{bmatrix}3&0\\1 & 2 \end{bmatrix}\) dan \(\textbf{D} = \begin{bmatrix}-2&1\\4 & -5 \end{bmatrix}\). Tentukan \(|\textbf{CD}|\)
\(|\textbf{C}| = \begin{vmatrix}3&0\\1 & 2 \end{vmatrix}\)
\(|\textbf{C}| = 3(2)\:-\:0(1)\)
\(|\textbf{C}| = 6\)
\(|\textbf{D}| = \begin{vmatrix}-2&1\\4 & -5 \end{vmatrix}\)
\(|\textbf{D}| = (-2)(-5)\:-\:1(4)\)
\(|\textbf{D}| = 10\:-\:4\)
\(|\textbf{D}| = 6\)
\(|\textbf{CD}| = |\textbf{C}| \cdot |\textbf{D}|\)
\(|\textbf{CD}| = 6\cdot 6\)
\(|\textbf{CD}| = 36\)
Soal 4
Diketahui \(\textbf{E} = \begin{bmatrix}3&4\\-5 & -6 \end{bmatrix}\). Tentukan \(|\textbf{E}^{-1}|\)
\(|\textbf{E}| = \begin{vmatrix}3&4\\-5 & -6 \end{vmatrix}\)
\(|\textbf{E}| = 3(-6)\:-\:4(-5)\)
\(|\textbf{E}| = -18 + 20\)
\(|\textbf{E}| = 2\)
\(|\textbf{E}^{-1}| = \dfrac{1}{|\textbf{E}|}\)
\(|\textbf{E}^{-1}| = \dfrac{1}{2}\)