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Question #66383

Difficulty: 8/10 | 🟢 Free

The Question

Let α\alpha and β\beta be the roots of the equation z2−(4+3i)z+(1+7i)=0z^2 - (4+3i)z + (1+7i) = 0, with ∣α∣>∣β∣|\alpha| > |\beta|. Let g:R→Cg: \mathbb{R} \to \mathbb{C} be defined as g(x)=αx+βg(x) = \alpha x + \beta. Consider the function f:C∖{α+β}→Cf: \mathbb{C} \setminus \{\alpha+\beta\} \to \mathbb{C} defined by f(z)=z2−(α+β)2zˉ−(α+β)‾f(z) = \frac{z^2 - (\alpha+\beta)^2}{\bar{z} - \overline{(\alpha+\beta)}} If L=lim⁡x→1f(g(x))L = \lim_{x \to 1} f(g(x)), find the value of 5Re(L)5 \text{Re}(L).

Options

  • A.

    28

  • B.

    14

  • C.

    40

  • D.

    -40

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Specialist

Targeted practice for niche, high-difficulty concepts that frequently appear in JEE Advanced exams.

Concepts Behind This Question

Limit Existence at Discontinuity|Composition Continuity|Quadratic Equations with Complex Coefficients

Why This Question Is Tricky

Examiner Levers

Recursive Logic

The answer to part A is required to solve part B (Step-wise failure test).

Difficulty Boost : +5

Common Mistakes

This question tests the existence of limits for complex functions at a discontinuity when composed with a real-variable function.

The primary trap is that lim⁡z→α+βf(z)\lim_{z \to \alpha+\beta} f(z) does not exist in the complex plane because the limit is path-dependent (it relies on the angle of approach).

Students might incorrectly conclude the limit LL does not exist or erroneously evaluate it along a standard path like the real axis (yielding 40).

However, because the inner function g(x)g(x) restricts the domain to x∈Rx \in \mathbb{R}, the approach to the discontinuity is locked along a specific line with direction α\alpha.

This fixed phase shift ααˉ\frac{\alpha}{\bar{\alpha}} must be accounted for, rewarding students who rigorously apply the definition of the composition rather than blindly applying L'Hôpital's rule or assuming path independence.

Quick Facts About This Question

Question Information

SubjectMathematics
ChapterContinuity and Differentiability - Class 12
ConceptLimit Existence at Discontinuity
Difficulty8
Cognitive Load7
Target Solve Time170 sec
AccessFree