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Let x=[(2, 1),(0, 3)] be a matrix. If X^...

Let `x=[(2, 1),(0, 3)]` be a matrix. If `X^(6)=[(a, b),(c,d)]`, then the number of divisors of `(a+b+2020c+d)` is equal to

A

7

B

14

C

21

D

28

Text Solution

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The correct Answer is:
To solve the problem, we need to find the matrix \( X^6 \) given the matrix \( X = \begin{pmatrix} 2 & 1 \\ 0 & 3 \end{pmatrix} \), and then compute the expression \( a + b + 2020c + d \) where \( X^6 = \begin{pmatrix} a & b \\ c & d \end{pmatrix} \). ### Step 1: Calculate \( X^2 \) To find \( X^6 \), we first calculate \( X^2 \): \[ X^2 = X \cdot X = \begin{pmatrix} 2 & 1 \\ 0 & 3 \end{pmatrix} \cdot \begin{pmatrix} 2 & 1 \\ 0 & 3 \end{pmatrix} \] Calculating the elements: - First row, first column: \( 2 \cdot 2 + 1 \cdot 0 = 4 \) - First row, second column: \( 2 \cdot 1 + 1 \cdot 3 = 5 \) - Second row, first column: \( 0 \cdot 2 + 3 \cdot 0 = 0 \) - Second row, second column: \( 0 \cdot 1 + 3 \cdot 3 = 9 \) Thus, \[ X^2 = \begin{pmatrix} 4 & 5 \\ 0 & 9 \end{pmatrix} \] ### Step 2: Calculate \( X^3 \) Next, we calculate \( X^3 = X^2 \cdot X \): \[ X^3 = \begin{pmatrix} 4 & 5 \\ 0 & 9 \end{pmatrix} \cdot \begin{pmatrix} 2 & 1 \\ 0 & 3 \end{pmatrix} \] Calculating the elements: - First row, first column: \( 4 \cdot 2 + 5 \cdot 0 = 8 \) - First row, second column: \( 4 \cdot 1 + 5 \cdot 3 = 19 \) - Second row, first column: \( 0 \cdot 2 + 9 \cdot 0 = 0 \) - Second row, second column: \( 0 \cdot 1 + 9 \cdot 3 = 27 \) Thus, \[ X^3 = \begin{pmatrix} 8 & 19 \\ 0 & 27 \end{pmatrix} \] ### Step 3: Calculate \( X^6 \) Now, we calculate \( X^6 = X^3 \cdot X^3 \): \[ X^6 = \begin{pmatrix} 8 & 19 \\ 0 & 27 \end{pmatrix} \cdot \begin{pmatrix} 8 & 19 \\ 0 & 27 \end{pmatrix} \] Calculating the elements: - First row, first column: \( 8 \cdot 8 + 19 \cdot 0 = 64 \) - First row, second column: \( 8 \cdot 19 + 19 \cdot 27 = 152 + 513 = 665 \) - Second row, first column: \( 0 \cdot 8 + 27 \cdot 0 = 0 \) - Second row, second column: \( 0 \cdot 19 + 27 \cdot 27 = 729 \) Thus, \[ X^6 = \begin{pmatrix} 64 & 665 \\ 0 & 729 \end{pmatrix} \] ### Step 4: Identify \( a, b, c, d \) From \( X^6 = \begin{pmatrix} a & b \\ c & d \end{pmatrix} \), we have: - \( a = 64 \) - \( b = 665 \) - \( c = 0 \) - \( d = 729 \) ### Step 5: Calculate \( a + b + 2020c + d \) Now we compute: \[ a + b + 2020c + d = 64 + 665 + 2020 \cdot 0 + 729 = 64 + 665 + 0 + 729 = 1458 \] ### Step 6: Find the number of divisors of 1458 To find the number of divisors of 1458, we first factor it: \[ 1458 = 2 \times 729 = 2 \times 3^6 \] The formula for the number of divisors based on the prime factorization \( p_1^{e_1} \times p_2^{e_2} \cdots \times p_n^{e_n} \) is: \[ (e_1 + 1)(e_2 + 1) \cdots (e_n + 1) \] For \( 1458 = 2^1 \times 3^6 \): - For \( 2^1 \): \( 1 + 1 = 2 \) - For \( 3^6 \): \( 6 + 1 = 7 \) Thus, the number of divisors is: \[ 2 \times 7 = 14 \] ### Final Answer The number of divisors of \( a + b + 2020c + d \) is \( \boxed{14} \).
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