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If alpha satisfies the equation x^2+x+1=0 and (1+alpha)^7=A+Balpha+Calpha^2, A, B, Cge 0, then 5(3A-2B-C) is equal to:

Numerical Answer Type:
Enter a numerical value Answer: 5 to 5 +4 marks

Solution & Explanation

### Related Formula 1 + omega + omega^2 = 0 omega^3 = 1 ### Core Logic The equation x^2 + x + 1 = 0 is the standard identity whose roots are the non-real cube roots of unity, omega and omega^2. Let us assign alpha = omega. We are given the expression (1+alpha)^7. Substituting the root: (1+omega)^7. ### Step 1: Simplify using Unity Properties From the identity 1 + omega + omega^2 = 0, we extract: 1 + omega = -omega^2 Substitute this into the expression: (1+omega)^7 = (-omega^2)^7 = -omega^14 ### Step 2: Cyclical Reduction Using omega^3 = 1, reduce the exponent 14 modulo 3: 14 = 3(4) + 2 Rightarrow omega^14 = (omega^3)^4 cdot omega^2 = 1 cdot omega^2 = omega^2 Thus, the expression reduces to -omega^2. Rewrite this back to its linear form using 1 + omega + omega^2 = 0: -omega^2 = 1 + omega = 1 + alpha ### Step 3: Finding Co-efficients We compare 1 + alpha with A + Balpha + Calpha^2. Notice that 1 + alpha can be directly represented without any alpha^2 term (and we must keep A, B, C ge 0). So, A = 1, B = 1, C = 0. ### Step 4: Final Output Evaluation Substitute these constants into the required equation 5(3A - 2B - C): 5(3(1) - 2(1) - 0) 5(3 - 2) = 5(1) = 5 ### Pattern Recognition The roots of x^2+x+1=0 are always omega, omega^2. Expressions of the form (1+omega)^k rapidly collapse down to single variables via the 1+omega+omega^2=0 rule, making multi-variable polynomial equations instantly trivial. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Complex Numbers

Reference Study Guides

More Complex Numbers Previous-Year Questions — Page 5

Q29 jee_main_2024_29_january_evening Integral Solutions
Let the set C = left\(x,y)mid x^2 -2^y = 2023, x,yin mathbbNright\. Then sum_(x,y)in C(x + y) is equal to
Numerical Answer. Answer: 46 to 46

Solution

### Related Formula Analyze structural equations through modular constraints (e.g., modulo 3 or 4) to limit potential bounds. ### Core Logic Given the equation: x^2 - 2^y = 2023. Let us inspect the numbers modulo 8: 2023 equiv 7 pmod 8 A perfect square x^2 can only be congruent to 0, 1, 4 pmod 8. * If y geq 3, then 2^y equiv 0 pmod 8 implies x^2 equiv 7 pmod 8, which is impossible. Therefore, y must be less than 3. Since y in mathbbN, the only choices are y = 1 or y = 2. ### Step 1: Testing Small Exponent Valuations * Case 1: y = 1 x^2 - 2^1 = 2023 implies x^2 = 2025 implies x = 45 quad (textsince 45^2 = 2025) This gives a valid natural solution pair: (45, 1). * Case 2: y = 2 x^2 - 2^2 = 2023 implies x^2 = 2027 Since 2027 is not a perfect square, this yields no natural solutions. Thus, the only valid point element inside set C is (45, 1). ### Step 2: Sum Evaluation Evaluating the required target accumulation: sum (x + y) = 45 + 1 = 46 ### Pattern Recognition Exponential Diophantine equations (equations with variables in exponents) are best analyzed using modular arithmetic constraints to quickly find small finite upper bounds. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Principle of Mathematical Induction / Number Theory
Q11 jee_main_2024_27_jan_morning Modulus and Conjugate
If S=\zin C:|z-i|=|z+i|=|z-1|\, then n(S) is:
  • A. 1
  • B. 0
  • C. 3
  • D. 2

Solution

### Related Formula |z - z_1| = |z - z_2| This represents the perpendicular bisector of the line segment joining the points z_1 and z_2 in the complex plane. ### Core Logic The given set defines a complex number z that is equidistant from three fixed points: A equiv (0, 1) corresponding to i B equiv (0, -1) corresponding to -i C equiv (1, 0) corresponding to 1 The condition |z-i|=|z+i|=|z-1| implies that z is the point of intersection of the perpendicular bisectors of the sides of the triangle formed by A, B, and C. ### Step 1: Finding the Circumcenter The point of intersection of the perpendicular bisectors of a triangle is its circumcenter. Since A(0,1), B(0,-1), and C(1,0) form a unique, non-degenerate triangle, they have exactly one unique circumcenter. ### Step 2: Final Conclusion Therefore, there is only one such complex number z that satisfies the condition. n(S) = 1 ### Pattern Recognition Recognize that |z - z_1| = |z - z_2| = |z - z_3| is geometrically identical to finding the circumcenter of a triangle with vertices at z_1, z_2, and z_3. A non-collinear set of three points always yields exactly 1 circumcenter. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Complex Numbers Class 11 Maths: Straight Lines
Q5 jee_main_2024_29_jan_morning Modulus and Equality of Complex Numbers
If z=frac12-2i, is such that |z+1|=alpha z+beta(1+i), i=sqrt-1 and alpha,betain R, then alpha+beta is equal to
  • A. -4
  • B. 3
  • C. 2
  • D. -1

Solution

### Related Formula |x + iy| = sqrtx^2 + y^2 Two complex numbers are equal if and only if their real and imaginary parts are respectively equal. ### Core Logic Given z = frac12 - 2i. Calculate |z + 1|: |z + 1| = left| left(frac12 - 2iright) + 1 right| = left| frac32 - 2i right| = sqrtleft(frac32right)^2 + (-2)^2 = sqrtfrac94 + 4 = sqrtfrac254 = frac52 Now substitute z and |z + 1| into the original equation: frac52 = alphaleft(frac12 - 2iright) + beta(1 + i) Expand and group real and imaginary components on the RHS: frac52 = left(fracalpha2 - 2alpha iright) + (beta + beta i) frac52 = left(fracalpha2 + betaright) + i(beta - 2alpha) ### Step 1: Equate Parts By equating the real and imaginary parts from both sides, we get a system of linear equations: Imaginary part: 0 = beta - 2alpha Rightarrow beta = 2alpha Real part: frac52 = fracalpha2 + beta Substitute beta = 2alpha into the real part equation: frac52 = fracalpha2 + 2alpha frac52 = frac5alpha2 alpha = 1 Using alpha = 1, find beta: beta = 2(1) = 2 ### Step 2: Final Calculation Calculate the final requested value: alpha + beta = 1 + 2 = 3 ### Pattern Recognition Equating complex parts reduces single complex equations into two simultaneous linear equations. Treat |z+1| strictly as a scalar magnitude and parse directly into algebraic components. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers and Quadratic Equations
Q23 jee_main_2024_29_jan_morning Higher Powers of Roots
Let alpha, beta be the roots of the equation x^2-x+2=0 with Im(alpha) gt Im(beta). Then alpha^6+alpha^4+beta^4-5alpha^2 is equal to
Numerical Answer. Answer: 13 to 13

Solution

### Related Formula Since alpha is a root of x^2 - x + 2 = 0, it must satisfy the equation exactly: alpha^2 - alpha + 2 = 0 Rightarrow alpha^2 = alpha - 2 This is an essential root reduction property allowing polynomials of high degrees to be collapsed linearly. ### Core Logic We need to evaluate the expression E = alpha^6 + alpha^4 + beta^4 - 5alpha^2. Use the substitution alpha^2 = alpha - 2 to iteratively depress the powers of alpha. alpha^4 = (alpha^2)^2 = (alpha - 2)^2 = alpha^2 - 4alpha + 4 Substitute alpha^2 = alpha - 2 again into the result: alpha^4 = (alpha - 2) - 4alpha + 4 = -3alpha + 2 Now, generate alpha^6 using alpha^4: alpha^6 = alpha^4 cdot alpha^2 = (-3alpha + 2)(alpha - 2) = -3alpha^2 + 6alpha + 2alpha - 4 = -3alpha^2 + 8alpha - 4 Substitute alpha^2 = alpha - 2 into the result again: alpha^6 = -3(alpha - 2) + 8alpha - 4 = -3alpha + 6 + 8alpha - 4 = 5alpha + 2 ### Step 1: Simplify the Full Expression The symmetry of the roots dictates that beta^4 behaves identically to alpha^4. Thus: beta^4 = -3beta + 2 Substitute all depressed linear forms back into E = alpha^6 + alpha^4 + beta^4 - 5alpha^2: E = (5alpha + 2) + (-3alpha + 2) + (-3beta + 2) - 5(alpha - 2) E = 5alpha - 3alpha - 5alpha - 3beta + 2 + 2 + 2 + 10 E = -3alpha - 3beta + 16 E = -3(alpha + beta) + 16 ### Step 2: Apply Sum of Roots From the original quadratic equation x^2 - x + 2 = 0, the sum of roots is: alpha + beta = -frac-11 = 1 Substitute this back: E = -3(1) + 16 = 13 (Note: The condition Im(alpha) gt Im(beta) was a distractor since the expression simplified perfectly symmetrically into alpha + beta without needing the individual complex values of the roots). ### Pattern Recognition Never compute De Moivre polar forms for high root powers unless the quadratic has roots like omega or i. Always use the characteristic quadratic relation alpha^2 = palpha + q to rapidly step down degrees until everything is strictly linear. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers and Quadratic Equations

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