Sigma Percentile
JEE Advanced 2009
LEVELJEE Main

Animated Solution for Mathematics - Complex Numbers: Let be a complex number where and are integers. Then the area of the rectangle whose vertices are the roots of the equation is

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Visualized Solution

Analyze the Equation

  • Given equation:
  • We need to find the roots of this equation in the complex plane.
  • The roots will form the vertices of a rectangle.

Factor the Equation

  • Notice the common terms in .
  • Factor out :

Introduce Cartesian Form

  • Let
  • The problem states and are integers ().

Evaluate

  • Recall the property of a complex number multiplied by its conjugate.

Evaluate

  • Expand
  • Expand
  • Add them:

Substitute Back

  • Substitute the evaluated expressions into .

Simplify the Equation

  • Divide both sides by :
  • Apply the difference of squares formula:

Analyze Integer Constraints

  • We need integers such that .
  • Let's list the first few fourth powers of integers:

Find and

  • Notice that .
  • Therefore, and .
  • This gives and .
  • So, and .

Identify the Vertices

  • The four combinations of give the four roots:
  • These are the vertices of our rectangle.

Determine the Dimensions

  • Length (parallel to real axis): Distance between and is .
  • Width (parallel to imaginary axis): Distance between and is .

Calculate the Final Area

  • The area of the rectangle is square units.

The Sigma Insight: Geometrical Applications of Complex Numbers

Solution Diagram
Welcome, future engineer. Today, we are not just solving an equation; we are embarking on a journey through the Argand plane.
When you first look at the equation , it might seem intimidating. It looks like a high-degree polynomial, and the thought of expanding it might make you want to reach for a calculator.
But hold on. In the world of JEE Advanced, the most complex-looking problems often hide the most elegant, simple solutions. Our goal is to peel back the layers of this equation until we find the geometric truth hidden underneath.

The Algebraic Dance

Let us start by observing the structure. We have .
Notice the symmetry? Both terms contain and . This is a classic invitation to factor.
If we pull out the common term , the equation transforms into:
Suddenly, the problem feels much lighter. We have reduced a high-degree expression into a product of two simpler components. This is the first step in mastering complex numbers: look for the structure before you start calculating.

The Cartesian Lens

Now, we introduce the Cartesian form, . But wait, look at the problem statement again. It tells us that and are integers.
This is the most critical piece of information. It changes the nature of the problem entirely. We are no longer solving for arbitrary complex numbers; we are hunting for integer coordinates.
Let us evaluate our pieces. We know that . This is a fundamental property that you should always keep in your toolkit.
Next, consider the term . When we expand , we get . When we expand , we get .
When we add them together, the imaginary parts and vanish into thin air. We are left with . This cancellation is the beauty of complex conjugates.

The Integer Constraint

Now, let us substitute these back into our factored equation:
Dividing both sides by , we get . If you recognize the difference of squares, you will see that this simplifies to:
This is where the integer constraint becomes our best friend. We are looking for two perfect fourth powers that differ by .
Let us list them: , , , , . Look at and . The difference is .
It fits perfectly! This implies and , which means and . Thus, and .

The Geometric Victory

We have found our coordinates. The roots are the four points and .
If you plot these on the complex plane, you will see a rectangle. The length of this rectangle, parallel to the real axis, is the distance between and , which is .
The width, parallel to the imaginary axis, is the distance between and , which is . The area of a rectangle is simply length times width.
So, . We have arrived at the solution. It was not about brute force; it was about identifying the symmetry, respecting the constraints, and letting the algebra guide us to the geometric reality.
The final area is 48.

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