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 Type:
Enter a numerical value Answer: 13 to 13 +4 marks

Solution & Explanation

### 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

Reference Study Guides

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Q26 jee_main_2024_31_jan_morning Properties of Modulus and Argument
If alpha denotes the number of solutions of |1 - i|^x = 2^x and beta = left(frac|z|arg(z)right), where z = fracpi4 (1 + i)^4 left(frac1 - sqrtpi isqrtpi + i + fracsqrtpi - i1 + sqrtpi iright), i = sqrt-1, then the distance of the point (alpha, beta) from the line 4x - 3y = 7 is
Numerical Answer. Answer: 3 to 3

Solution

### Core Logic |1 - i|^x = 2^x implies (sqrt2)^x = 2^x implies 2^x/2 = 2^x This implies fracx2 = x implies x = 0. There is exactly 1 solution, so alpha = 1. ### Step 1: Simplify complex number z (1+i)^4 = ((1+i)^2)^2 = (1 + i^2 + 2i)^2 = (2i)^2 = -4 Thus, z = -pi left( frac(1-sqrtpii)(sqrtpi-i)pi + 1 + frac(sqrtpi-i)(1-sqrtpii)1 + pi right) ### Step 2: Simplify Bracket Let's expand the terms directly: z = fracpi4(-4) left[ fracsqrtpi - pi i - i - sqrtpipi + 1 + fracsqrtpi - i - pi i - sqrtpi1 + pi right] = -pi left[ frac-i(pi+1)pi+1 + frac-i(pi+1)pi+1 right] = -pi [ -i - i ] = 2pi i ### Step 3: Find beta For z = 2pi i: |z| = 2pi and arg(z) = fracpi2. beta = frac|z|arg(z) = frac2pipi/2 = 4 ### Step 4: Distance from Line Distance of point (alpha, beta) = (1, 4) from the line 4x - 3y - 7 = 0: D = frac|4(1) - 3(4) - 7|sqrt4^2 + (-3)^2 = frac|4 - 12 - 7|5 = frac|-15|5 = 3 ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Complex Numbers and Quadratic Equations Class 11 Maths: Straight Lines

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