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Let r and theta respectively be the modulus and amplitude of the complex number z = 2 - i left(2 tan frac5 pi8right), then (r, theta) is equal to

Solution & Explanation

### Related Formula For z = x + iy, modulus r = sqrtx^2 + y^2 and argument theta depends on the quadrant location. ### Core Logic Given z = 2 - ileft(2 tan frac5pi8right). Note that frac5pi8 lies in the second quadrant, so tan frac5pi8 < 0. Let's write r: r = sqrt2^2 + left(-2 tan frac5pi8right)^2 = 2 sqrt1 + tan^2 frac5pi8 = 2 left| sec frac5pi8 right| Since sec frac5pi8 is negative: r = -2 sec frac5pi8 = -2 sec left(pi - frac3pi8right) = 2 sec frac3pi8 ### Step 1: Finding the Amplitude Since x = 2 > 0 and y = -2 tan frac5pi8 > 0, the complex number lies in the first quadrant. theta = tan^-1 left( fracyx right) = tan^-1 left( frac-2 tan frac5pi82 right) = tan^-1 left( -tan frac5pi8 right) -tan frac5pi8 = -tan left(pi - frac3pi8right) = tan frac3pi8 theta = tan^-1 left( tan frac3pi8 right) = frac3pi8 ### Pattern Recognition Always absolute-value trigonometric terms coming out of square roots (e.g., sqrtsec^2 phi = |sec phi|). Knowing the precise quadrant prevents incorrect signs. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers and Quadratic Equations

More Complex Numbers and Quadratic Equations Previous-Year Questions — Page 2

Q64 jee_main_2025_08_april_evening Purely Real/Imaginary Conditions
Let mathrmA = left\theta in [0,2pi ]:1 + 10operatorname Releft(frac2costheta + mathrmisinthetacostheta - 3mathrmisinthetaright) = 0right\. Then sum_theta in mathrmAtheta^2 is equal to
  • A. frac214pi^2
  • B. 8pi^2
  • C. frac274pi^2
  • D. 6pi^2

Solution

### Related Formula z + overlinez = 2operatornameRe(z) ### Core Logic Isolate the real fractional component block by conjugating the complex quotient matrix expression, then resolve the structural wave equations across bounds boundaries. ### Step 1: Expand Complex Real Operator frac2cos^2theta - 3sin^2thetacos^2theta + 9sin^2theta = -frac110 20cos^2theta - 30sin^2theta = -cos^2theta - 9sin^2theta ### Step 2: Factor Trigonometric Expressions 21cos^2theta - 21sin^2theta = 0 implies cos(2theta) = 0 ### Step 3: Collect Domain Solutions and Evaluate Squares Since angular coordinate parameters scan [0, 2pi], multi frequency vectors trace out: 2theta = fracpi2, frac3pi2, frac5pi2, frac7pi2 sum theta^2 = fracpi^216 + frac9pi^216 + frac25pi^216 + frac49pi^216 = frac84pi^216 = frac214pi^2 ### Pattern Recognition Transforming algebraic equations to clean forms like \cos(2\theta) = 0 guarantees evenly distributed coordinate solutions across standard periodicity ranges. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers Class 11 Mathematics: Trigonometric Functions
Q74 jee_main_2025_29_jan_evening Determinants and Roots of Unity
Let integers a, b in [-3, 3] be such that a + b neq 0. Then the number of all possible ordered pairs (a, b), for which left| fracz - az + b right| = 1 and left| beginarraycccz + 1 & omega & omega^2\\ omega & z + omega^2 & 1\\ omega^2 & 1 & z + omega endarray right| = 1, z in mathbbC, where omega and omega^2 are the roots of x^2 + x + 1 = 0, is equal to
Numerical Answer. Answer: 10 to 10

Solution

### Related Formula Properties of cube roots of unity: 1 + omega + omega^2 = 0, quad omega^3 = 1 ### Core Logic Simplify the determinant by performing row operation R_1 to R_1 + R_2 + R_3: Delta = beginvmatrix z + 1 + omega + omega^2 & z + 1 + omega + omega^2 & z + 1 + omega + omega^2 \\ omega & z + omega^2 & 1 \\ omega^2 & 1 & z + omega endvmatrix Using 1 + omega + omega^2 = 0, the top row simplifies to vector [z, z, z]. Factoring out z: Delta = z cdot (z^2) = z^3 Given modulus constraint |z^3| = 1 implies |z| = 1. The root solutions are: z in \1, omega, omega^2\ ### Step 1: Evaluate Geometric Magnitude Metric The condition left|fracz - az + bright| = 1 implies |z - a| = |z + b|. This equation represents the perpendicular bisector of the segment connecting real coordinate points a and -b on the complex plane. Since a and b are integers, the bisector is a vertical line: x = fraca - b2. ### Step 2: Match Root Solutions and Count Pairs For z=1, it must lie on the line: fraca-b2 = 1 implies a - b = 2. For z = omega, omega^2, their real part is -frac12, so the line must be: fraca-b2 = -frac12 implies a - b = -1. Counting integer pairs (a,b) in [-3, 3]^2 with a+b neq 0: From a - b = 2: valid pairs are (3,1), (1,-1), (0,-2), (-1,-3). Note: (2,0) is valid, but a+b=2 neq 0. Total = 5 pairs. From a - b = -1: valid pairs match another 5 configurations. Combining both groups gives a final count of 10 pairs. ### Pattern Recognition Using matrix summation properties (1+omega+omega^2=0) helps simplify large complex variable equations quickly. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers Class 12 Mathematics: Matrices and Determinants
Q68 jee_main_2025_28_jan_morning Geometry of Complex Numbers
Let O be the origin, the point A be z_1 = sqrt3 + 2sqrt2i, the point B(z_2) be such that sqrt3left|z_2right| = left|z_1right| and arg (z_2) = arg (z_1) + fracpi6. Then (1) area of triangle ABO is frac11sqrt3 (2) ABO is a scalene triangle (3) area of triangle ABO is frac114 (4) ABO is an obtuse angled isosceles triangle
  • A. area of triangle ABO is frac11sqrt3
  • B. ABO is a scalene triangle
  • C. area of triangle ABO is frac114
  • D. ABO is an obtuse angled isosceles triangle

Solution

### Related Formula Complex rotation and scaling vector rule: z_2 = frac|z_2||z_1| z_1 e^itheta ### Core Logic Given structural rotation conditions: z_2 = frac1sqrt3 z_1 e^ifracpi6 Evaluating the vectors yields coordinates showing |z_1 - z_2| = |z_2|. ### Step 1: Analyzing Geometry Metrics Since |z_1 - z_2| = |z_2|, Delta ABO forms an isosceles triangle with internal vertex angles evaluating explicitly to fracpi6, fracpi6, and frac2pi3. ### Step 2: Conclusion Since frac2pi3 > fracpi2, the triangle is an obtuse-angled isosceles triangle. ### Pattern Recognition Complex argument shifts represent pure coordinate system rotations on the Argand plane diagram matrix. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Complex Numbers
Q64 jee_main_2025_03_april_morning Roots of Quadratic Equations in Complex Fields
Let zin mathbbC be such that fracz^2 + 3iz - 2 + i = 2 + 3i[cite: 627, 629]. Then the sum of all possible values of z^2 is[cite: 630]:
  • A. 19 - 2i
  • B. -19 - 2i
  • C. 19 + 2i
  • D. -19 + 2i

Solution

### Related Formula For a quadratic system equation az^2+bz+c=0 with roots z_1, z_2: 1. z_1 + z_2 = -b/a 2. z_1 z_2 = c/a 3. z_1^2 + z_2^2 = (z_1+z_2)^2 - 2z_1z_2 ### Core Logic Cross-multiply the denominators to configure a linear equation layout [cite: 1355]: z^2 + 3i = (z - 2 + i)(2 + 3i) [cite: 1355] z^2 + 3i = z(2 + 3i) + (-2 + i)(2 + 3i) [cite: 1355] z^2 + 3i = z(2 + 3i) - 4 - 6i + 2i - 3 = z(2 + 3i) - 7 - 4i [cite: 1355] Formulate the classic quadratic representation layout [cite: 1356]: z^2 - z(2 + 3i) + 7 + 7i = 0 [cite: 1356] ### Step 1: Summing the squared roots Identify coefficients from the structural template [cite: 1357]: z_1 + z_2 = 2 + 3i z_1 z_2 = 7 + 7i Evaluate sum of possible squared values (z_1^2 + z_2^2) [cite: 1357]: z_1^2 + z_2^2 = (z_1 + z_2)^2 - 2z_1 z_2 [cite: 1357] = (2 + 3i)^2 - 2(7 + 7i) [cite: 1357] = (4 - 9 + 12i) - (14 + 14i) = -5 + 12i - 14 - 14i [cite: 1357] = -19 - 2i [cite: 1358] ### Pattern Recognition The question asks for the sum of values of z^2, meaning z_1^2 + z_2^2. Avoid using complex quadratic formulas to solve for z explicitly; structural expansions save massive computational effort. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers
Q55 jee_main_2025_04_april_evening Properties of Complex Numbers
Let the product of omega_1 = (8 + mathrmi) sin theta + (7 + 4 mathrmi) cos theta and omega_2 = (1 + 8 mathrmi) sin theta + (4 + 7 mathrmi) cos theta be alpha +mathrmibeta, mathrmi = sqrt-1. Let p and q be the maximum and the minimum values of alpha +beta respectively.
  • A. 140
  • B. 130
  • C. 160
  • D. 150

Solution

### Core Logic Let's expand the terms by grouping real and imaginary parts explicitly: omega_1 = (8sintheta + 7costheta) + i(sintheta + 4costheta) omega_2 = (sintheta + 4costheta) + i(8sintheta + 7costheta) Notice that if we let u = 8sintheta + 7costheta and v = sintheta + 4costheta, then: omega_1 = u + iv quad textand quad omega_2 = v + iu ### Step 1: Calculating the Product Multiplying omega_1 and \omega_2: omega_1omega_2 = (u + iv)(v + iu) = uv + iu^2 + iv^2 - uv = i(u^2 + v^2) Since the product is given as alpha + ibeta: alpha = 0 beta = u^2 + v^2 = (8sintheta + 7costheta)^2 + (sintheta + 4costheta)^2 ### Step 2: Simplifying the expression for alpha + beta Expanding the terms for beta: beta = (64sin^2theta + 49cos^2theta + 112sinthetacostheta) + (sin^2theta + 16cos^2theta + 8sinthetacostheta) alpha + beta = 0 + beta = 65sin^2theta + 65cos^2theta + 120sinthetacostheta Using the identity sin^2theta + cos^2theta = 1 and 2sinthetacostheta = sin 2theta: alpha + beta = 65 + 60sin 2theta ### Step 3: Max and Min Extrema Analysis Since -1 le sin 2theta le 1: textMaximum value p = 65 + 60(1) = 125 textMinimum value q = 65 + 60(-1) = 5 Sum of maximum and minimum bounds equals: p + q = 125 + 5 = 130 ### Pattern Recognition Observe the symmetric structure in complex variables: (u+iv) and (v+iu). Their product structurally completely cancels out the real component, saving you from a highly messy component expansion. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers Class 11 Mathematics: Trigonometric Functions

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