We are given a set of \(2 \times 2\) matrices \( \text{A} = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \) with elements \( a, b, c, d \in \{0, 1, 2, 3, 4\} \), satisfying the equation:
\(A^2 - 4A + 3I = 0\)
We need to find the number of matrices in this set for which the sum of the diagonal elements (\(a + d\)) is equal to 4.
Step-by-Step Solution:
- Substitute \(\text{A}\) and calculate \(\text{A}^2\):
- \(\text{A} = \begin{bmatrix} a & b \\ c & d \end{bmatrix}\)
- \(\text{A}^2 = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \begin{bmatrix} a & b \\ c & d \end{bmatrix} = \begin{bmatrix} a^2 + bc & ab + bd \\ ac + cd & bc + d^2 \end{bmatrix}\)
- Given equation is:
- This simplifies to two equations:
- \(a^2 + bc - 4a + 3 = 0\)
- \(ab + bd - 4b = 0\)
- \(ac + cd - 4c = 0\)
- \(bc + d^2 - 4d + 3 = 0\)
- Considering the condition \(a + d = 4\).
- Substitute \(d = 4 - a\) into the equations as follows:
- \[a^2 + bc - 4a + 3 = 0 \quad \text{and} \quad bc + (4-a)^2 - 4(4-a) + 3 = 0\]
- This condition significantly reduces the possibilities. Try possible integer values:
- Values for \(a\) and \(d = 4-a\) are:
- \(a = 0, d = 4\)
- \(a = 1, d = 3\)
- \(a = 2, d = 2\)
- \(a = 3, d = 1\)
- \(a = 4, d = 0\)
- For each, solve for \(b\) and \(c\) using the equations above:
- After verifying each case, we find a total of 19 matrices satisfy these conditions.
Hence, the number of matrices in the set \(S\) for which the sum of the diagonal elements is 4 is 19.
Similar Questions
Let S be the set of the first 11 natural numbers. Then the number of elements in $A = \{B \subseteq S : n(B) \geq 2$ and the product of all elements of B is even is ________.
- The number of $3 \times 2$ matrices A, which can be formed using the elements of the set $\{-2, -1, 0, 1, 2\}$ such that the sum of all the diagonal elements of $A^T A$ is 5, is ______
- The number of numbers greater than 5000, less than 9000 and divisible by 3, that can be formed using the digits 0, 1, 2, 5, 9, if the repetition of the digits is allowed, is ______
- Let $z = (1 + i)(1 + 2i)(1 + 3i) \dots (1 + ni)$, where $i = \sqrt{-1}$. If $|z|^2 = 44200$, then $n$ is equal to _______
- Let $S = \{(m, n) : m, n \in \{1, 2, 3, \dots, 50\}\}$. If the number of elements $(m, n)$ in S such that $6^m + 9^n$ is a multiple of 5 is p and the number of elements $(m, n)$ in S such that $m + n$ is a square of a prime number is q, then $p + q$ is equal to ____________.
- Let $a_1 = 1$ and for $n \ge 1, a_{n+1} = \frac{1}{2} a_n + \frac{n^2 - 2n - 1}{n^2(n+1)^2}$. Then $\left| \sum_{n=1}^\infty \left( a_n - \frac{2}{n^2} \right) \right|$ is equal to ____________.
If $ \left(\frac{1}{^{15}C_0} + \frac{1}{^{15}C_1}\right)$ $\left(\frac{1}{^{15}C_1} + \frac{1}{^{15}C_2}\right)$ $\dots$ $ \left(\frac{1}{^{15}C_{12}} + \frac{1}{^{15}C_{13}}\right)$ = $\frac{\alpha^{13}}{^{14}C_0 ^{14}C_1 \dots ^{14}C_{12}} $, then $30\alpha$ is equal to __________.
- Three persons enter in a lift at the ground floor. The lift will go upto 10$^{\text{th}}$ floor. The number of ways, in which the three persons can exit the lift at three different floors, if the lift does not stop at first, second and third floors, is equal to _________.
- The number of 4-letter words, with or without meaning, which can be formed using the letters PQR PQRSTUVP, is ___________.
- Let $|A| = 6$, where A is a $3 \times 3$ matrix. If $|\text{adj}(3\text{adj}(A^2 \cdot \text{adj}(2A)))| = 2^m \cdot 3^n$, $m, n \in \mathbf{N}$, then $m + n$ is equal to ___________.
Important Questions from Algebra
Let S be the set of the first 11 natural numbers. Then the number of elements in $A = \{B \subseteq S : n(B) \geq 2$ and the product of all elements of B is even is ________.
- The number of $3 \times 2$ matrices A, which can be formed using the elements of the set $\{-2, -1, 0, 1, 2\}$ such that the sum of all the diagonal elements of $A^T A$ is 5, is ______
- The number of numbers greater than 5000, less than 9000 and divisible by 3, that can be formed using the digits 0, 1, 2, 5, 9, if the repetition of the digits is allowed, is ______
- Let $z = (1 + i)(1 + 2i)(1 + 3i) \dots (1 + ni)$, where $i = \sqrt{-1}$. If $|z|^2 = 44200$, then $n$ is equal to _______
- Let $S = \{(m, n) : m, n \in \{1, 2, 3, \dots, 50\}\}$. If the number of elements $(m, n)$ in S such that $6^m + 9^n$ is a multiple of 5 is p and the number of elements $(m, n)$ in S such that $m + n$ is a square of a prime number is q, then $p + q$ is equal to ____________.
