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Let M and m respectively be the maximum and the minimum values of f (x) = left| beginarrayc c c 1 + sin^ 2 x & cos^ 2 x & 4 sin 4 x \\ sin^ 2 x & 1 + cos^ 2 x & 4 sin 4 x \\ sin^ 2 x & cos^ 2 x & 1 + 4 sin 4 x endarray right|, x in R Then mathbfM^4 -mathbfm^4 is equal to :

Solution & Explanation

### Related Formula sin^2 x + cos^2 x = 1 -1 le sin 4x le 1 ### Core Logic Apply the row operations R_2 to R_2 - R_1 and R_3 to R_3 - R_1 to simplify the determinant: f(x) = left| beginarrayc c c 1 + sin^ 2 x & cos^ 2 x & 4 sin 4 x \\ -1 & 1 & 0 \\ -1 & 0 & 1 endarray right| ### Step 1: Expand the Determinant Expanding along the first row: f(x) = (1 + sin^2 x)(1 - 0) - cos^2 x(-1 - 0) + 4sin 4x(0 - (-1)) f(x) = 1 + sin^2 x + cos^2 x + 4sin 4x Since sin^2 x + cos^2 x = 1, we get: f(x) = 2 + 4sin 4x ### Step 2: Find Maximum and Minimum Values The range of sin 4x is [-1, 1]. M = 2 + 4(1) = 6 m = 2 + 4(-1) = -2 ### Step 3: Calculate M^4 - m^4 M^4 - m^4 = 6^4 - (-2)^4 = 1296 - 16 = 1280 ### Pattern Recognition Look for repeated structures or cyclic additions in rows. Subtracting rows quickly creates zeros, reducing complex trigonometric matrices into elementary algebraic expressions. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants Class 11 Mathematics: Trigonometric Functions

Reference Study Guides

More Matrices and Determinants Previous-Year Questions — Page 6

Q70 2025 Cofactors and Determinant Value
Let mathrmA = left[mathbfa_mathrmijright] = beginbmatrix log_5128 & log_45 \\ log_58 & log_425 endbmatrix . If A_ij is the cofactor of a_ij , C_ij = sum_k=1^2 a_ik A_jk , 1 leq i, j leq 2 , and C = [C_ij] , then 8|C| is equal to:
  • A. 262
  • B. 288
  • C. 242
  • D. 222

Solution

### Related Formula sum_k a_ik A_jk = delta_ij |A| implies C = beginbmatrix |A| & 0 \\ 0 & |A| endbmatrix implies |C| = |A|^2 ### Core Logic Evaluate the determinant of matrix A: |A| = (log_5 128)(log_4 25) - (log_4 5)(log_5 8) Using change of base rules: |A| = left(7log_5 2right)left(2log_4 5right) - left(frac12log_2 5right)left(3log_5 2right) |A| = 14left(log_5 2 cdot frac12log_2 5right) - frac32 = 7 - 1.5 = 5.5 = frac112 ### Step 1: Compute |C| and evaluate response target Since matrix properties dictate |C| = |A|^2: |C| = left(frac112right)^2 = frac1214 Evaluate targeted multiplier: 8|C| = 8 times frac1214 = 2 times 121 = 242 ### Pattern Recognition Recognize the core cofactor theorem identity instantly: multiplying rows by cofactors of other rows creates zero elements, yielding basic diagonal scalar structures matching matrix attributes. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Matrices and Determinants

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