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

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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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