If the system of linear equations 3x + y + beta z = 3 2x + alpha y - z = -3 x + 2y + z = 4 has infinitely many solutions, then the value of 22beta - 9alpha is:

Solution & Explanation

### Related Formula Cramer's Rule for infinite solutions specifies that the main determinant and all component determinants must vanish: Delta = 0 quad textand quad Delta_1 = Delta_2 = Delta_3 = 0 ### Core Logic Set the key system determinants to zero to form equations linking alpha and beta, then isolate the constants. ### Step 1: Set Main Determinant to Zero Delta = beginvmatrix 3 & 1 & beta \\ 2 & alpha & -1 \\ 1 & 2 & 1 endvmatrix = 0 Expand along the first row: 3(alpha + 2) - 1(2 + 1) + beta(4 - alpha) = 0 3alpha + 6 - 3 + 4beta - alphabeta = 0 implies 3alpha + 4beta - alphabeta + 3 = 0 quad dots (1) ### Step 2: Set Subsidiary Determinant to Zero Using Delta_3 = 0 by substituting the constants vector into the third column: Delta_3 = beginvmatrix 3 & 1 & 3 \\ 2 & alpha & -3 \\ 1 & 2 & 4 endvmatrix = 0 Expand along the first row: 3(4alpha + 6) - 1(8 + 3) + 3(4 - alpha) = 0 12alpha + 18 - 11 + 12 - 3alpha = 0 implies 9alpha + 19 = 0 implies alpha = -frac199 ### Step 3: Solve for Beta and Final Expression Substitute alpha = -frac199 into equation (1): 3left(-frac199right) + 4beta - left(-frac199right)beta + 3 = 0 -frac193 + 3 + betaleft(4 + frac199right) = 0 implies -frac103 + betaleft(frac559right) = 0 frac559beta = frac103 implies beta = frac103 cdot frac955 = frac611 Now compute 22beta - 9alpha: 22left(frac611right) - 9left(-frac199 ight) = 12 + 19 = 31 ### Pattern Recognition Choosing Delta_3 over Delta_1 or Delta_2 eliminates beta entirely because the variable parameters are localized in specific positions. This yields alpha directly without requiring a coupled system solution. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants

More Matrices and Determinants Previous-Year Questions — Page 3

Q52 jee_main_2025_08_april_evening System of Linear Equations
Let alpha be a solution of x^2 + x + 1 = 0, and for some a and b in mathbbR, [4 quad a quad b]beginbmatrix1 & 16 & 13\\ -1 & -1 & 2\\ -2 & -14 & -8 endbmatrix = [0 quad 0 quad 0]. If frac4alpha^4 + fracmalpha^a + fracnalpha^b = 3, then m + n is equal to
  • A. 3
  • B. 11
  • C. 7
  • D. 8

Solution

### Related Formula alpha^2 + alpha + 1 = 0 implies alpha = omega quad textwhere omega^3 = 1 ### Core Logic Perform row-matrix vector multiplication to generate a system of linear equations in a and b. Solve for the powers and reduce the algebraic equation using complex roots of unity. ### Step 1: Solve Matrix Vector Multiplication 4 - a - 2b = 0 64 - a - 14b = 0 52 + 2a - 8b = 0 From the first two equations, subtracting them gives: 60 - 12b = 0 implies b = 5 Substituting b = 5 into the first equation: 4 - a - 10 = 0 implies a = -6 ### Step 2: Evaluate Exponential Equation with Roots of Unity Substitute a = -6, b = 5 into the given equation: frac4alpha^4 + fracmalpha^-6 + fracnalpha^5 = 3 implies frac4omega + m + fracnomega^2 = 3 4omega^2 + m + nomega = 3 ### Step 3: Resolve Real and Imaginary Components Substitute standard values omega = -frac12 + fracsqrt32i and omega^2 = -frac12 - fracsqrt32i: 4left(-frac12 - fracsqrt32iright) + m + nleft(-frac12 + fracsqrt32iright) = 3 Equating the imaginary components: frac-4sqrt32 + fracnsqrt32 = 0 implies n = 4 Equating the real components: -2 + m - fracn2 = 3 implies -2 + m - 2 = 3 implies m = 7 m + n = 7 + 4 = 11 ### Pattern Recognition Whenever an expression satisfies Aomega^2 + Bomega + C = 0, it directly maps to a comparison with the standard identity omega^2 + omega + 1 = 0 up to a linear translation shift. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants Class 11 Mathematics: Complex Numbers
Q69 jee_main_2025_08_april_evening Determinant Properties of Adjoint
Let mathrmA = beginbmatrix 2 & 2 + mathrmp & 2 + mathrmp + mathrmq \\ 4 & 6 + 2mathrmp & 8 + 3mathrmp + 2mathrmq \\ 6 & 12 + 3mathrmp & 20 + 6mathrmp + 3mathrmq endbmatrix. If det left( adj(adj(3A)) right) = 2^m cdot 3^n, m, n in mathbbN, then m + n is equal to
  • A. 22
  • B. 24
  • C. 26
  • D. 20

Solution

### Related Formula |operatornameadj(operatornameadj(M))| = |M|^(n-1)^2 |kM| = k^n|M| ### Core Logic Perform determinant row reduction transforms to decouple tracking metrics p and q, leaving a baseline numerical determinant value behind. ### Step 1: Simplify the Determinant of Matrix A Execute columns adjustments: C_3 rightarrow C_3 - C_2 - C_1 times fracq2, then C_2 rightarrow C_2 - C_1 times left(1 + fracp2right): |A| = beginvmatrix 2 & 0 & 0 \\ 4 & 2 & 2+p \\ 6 & 6 & 8+3p endvmatrix = 2left(16 + 6p - 12 - 6pright) = 8 = 2^3 ### Step 2: Apply Adjoint Exponent Transforms For a matrix of dimensional profile size 3: |operatornameadj(operatornameadj(3A))| = |3A|^(3-1)^2 = |3A|^4 ### Step 3: Resolve Exponential System Size |3A| = 3^3 |A| = 3^3 times 2^3 |3A|^4 = (3^3 times 2^3)^4 = 2^12 times 3^12 Matching base parameter targets: m = 12, n = 12 implies m + n = 24 ### Pattern Recognition Linear parameter shifts down secondary column profiles usually dissolve cleanly during forward element elimination column steps. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants
Q61 jee_main_2025_29_jan_evening System of Linear Equations
Let alpha, beta ( alpha neq beta ) be the values of m, for which the equations x + y + z = 1 ; x + 2y + 4z = m and x + 4y + 10z = m^2 have infinitely many solutions. Then the value of sum_n=1^10 (n^alpha + n^beta) is equal to:
  • A. 440
  • B. 3080
  • C. 3410
  • D. 560

Solution

### Related Formula Cramer's rule for infinite solutions in a 3 variable system requires: Delta = Delta_x = Delta_y = Delta_z = 0 ### Core Logic Set up the primary matrix determinant Delta: Delta = beginvmatrix 1 & 1 & 1 \\ 1 & 2 & 4 \\ 1 & 4 & 10 endvmatrix = 1(20 - 16) - 1(10 - 4) + 1(4 - 2) = 4 - 6 + 2 = 0 Since Delta = 0 is true independent of m, analyze secondary delta constraints to maintain consistency for infinite paths. ### Step 1: Compute Dependent Variable Constraints Evaluate Delta_x = 0: Delta_x = beginvmatrix 1 & 1 & 1 \\ m & 2 & 4 \\ m^2 & 4 & 10 endvmatrix = 0 1(20 - 16) - 1(10m - 4m^2) + 1(4m - 2m^2) = 0 4 - 10m + 4m^2 + 4m - 2m^2 = 0 2m^2 - 6m + 4 = 0 implies m^2 - 3m + 2 = 0 Thus, m = 1, 2, which gives alpha = 1, beta = 2. ### Step 2: Calculate Sigma Expression sum_n=1^10 (n^1 + n^2) = sum_n=1^10 n + sum_n=1^10 n^2 = frac10(11)2 + frac10(11)(21)6 = 55 + 385 = 440 ### Pattern Recognition When infinitely many solutions are required, solving the determinant created by replacing one column with the constant vector provides parameter roots directly. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants
Q62 jee_main_2025_29_jan_evening Matrix Multiplication and Powers
Let mathbfA = [a_ij] be a matrix of order 3 times 3, with a_ij = left(sqrt2right)^i+j. If the sum of all the elements in the third row of A^2 is alpha + beta sqrt2, alpha, beta in mathbfZ, then alpha + beta is equal to
  • A. 280
  • B. 168
  • C. 210
  • D. 224

Solution

### Related Formula Element formula entry rule: a_ij = (sqrt2)^i+j ### Core Logic Constructing the initial matrix structure from the formula entries: A = beginbmatrix 2 & 2sqrt2 & 4 \\ 2sqrt2 & 4 & 4sqrt2 \\ 4 & 4sqrt2 & 8 endbmatrix Factoring scalar factor 4 out to ease squaring multiplication lines: A = 2beginbmatrix 1 & sqrt2 & 2 \\ sqrt2 & 2 & 2sqrt2 \\ 2 & 2sqrt2 & 4 endbmatrix ### Step 1: Calculate Rows of Power Matrix Squaring matrix A^2 matches scalar multipliers: A^2 = 4 beginbmatrix 1 & sqrt2 & 2 \\ sqrt2 & 2 & 2sqrt2 \\ 2 & 2sqrt2 & 4 endbmatrix beginbmatrix 1 & sqrt2 & 2 \\ sqrt2 & 2 & 2sqrt2 \\ 2 & 2sqrt2 & 4 endbmatrix Extract third row entries explicitly: textRow 3 = 4 beginbmatrix (2+4+8) & (2sqrt2+4sqrt2+8sqrt2) & (4+8+16) endbmatrix = 4 beginbmatrix 14 & 14sqrt2 & 28 endbmatrix ### Step 2: Aggregate Entries textSum of row elements = 4(14 + 14sqrt2 + 28) = 4(42 + 14sqrt2) = 168 + 56sqrt2 Matching structural parameters: alpha = 168, quad beta = 56 alpha + beta = 168 + 56 = 224 ### Pattern Recognition Pull common scaling scalar integers out of matrices before running large multiplications. It eliminates algebraic tracking errors across geometric indices. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants
Q71 jee_main_2025_28_jan_morning Symmetric and Skew Symmetric Matrices
Let M denote the set of all real matrices of order 3 times 3 and let S = \-3, -2, -1, 1, 2\. Let S_1 = left\A = left[ a_ij right] in M: A = A^T text and a_ij in S, forall i, j right\ S_2 = left\A = left[ a_ij right] in M: A = -A^T text and a_ij in S, forall i, j right\ S_3 = left\A = left[ a_ij right] in M: a_11 + a_22 + a_33 = 0 text and a_ij in S, forall i, j right\ If n(S_1 cup S_2 cup S_3) = 125alpha, then alpha equals.
Numerical Answer. Answer: 1613 to 1613

Solution

### Related Formula Set Principle of Inclusion-Exclusion: n(S_1 cup S_2 cup S_3) = n(S_1) + n(S_2) + n(S_3) - n(S_1 cap S_2) - n(S_2 cap S_3) - n(S_1 cap S_3) + n(S_1 cap S_2 cap S_3) ### Core Logic Let's count each subset based on the 5 elements available in S: 1. For S_1 (Symmetric matrices): 6 independent element choices implies n(S_1) = 5^6. 2. For S_2 (Skew-symmetric matrices): Diagonal elements must be 0, but 0 notin S, so n(S_2) = 0. Since n(S_2) = 0, any intersection term involving S_2 also becomes 0. ### Step 1: Calculating Trace Matrix Variations For S_3 (Trace equal to zero conditions): The condition a_11 + a_22 + a_33 = 0 over S = \-3, -2, -1, 1, 2\ has exactly 12 valid tuple combinations. The remaining 6 elements can be chosen freely. n(S_3) = 12 times 5^6 For the intersection n(S_1 cap S_3): n(S_1 cap S_3) = 12 times 5^3 ### Step 2: Final Inclusion-Exclusion Assembly n(S_1 cup S_2 cup S_3) = 5^6 + 12 times 5^6 - 12 times 5^3 = 5^3 times [13 times 5^3 - 12] = 125 times 1613 Thus, alpha = 1613. ### Pattern Recognition Always check if the set contains 0. Missing zero elements in skew-symmetric matrix setups instantly zeros out large blocks of permutations. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Maths: Matrices and Determinants
Rankbit System
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