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 zzˉ3+zˉz3=350, 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 zzˉ3+zˉz3=350.
Notice the symmetry? Both terms contain z and zˉ. This is a classic invitation to factor.
If we pull out the common term zzˉ, 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, z=x+iy. But wait, look at the problem statement again. It tells us that x and y 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 zzˉ=∣z∣2=x2+y2. This is a fundamental property that you should always keep in your toolkit.
Next, consider the term z2+zˉ2. When we expand z2=(x+iy)2, we get x2−y2+2ixy. When we expand zˉ2=(x−iy)2, we get x2−y2−2ixy.
When we add them together, the imaginary parts 2ixy and −2ixy vanish into thin air. We are left with 2(x2−y2). 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 2, we get (x2+y2)(x2−y2)=175. 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 175.
Let us list them: 14=1, 24=16, 34=81, 44=256, 54=625. Look at 256 and 81. The difference is 256−81=175.
It fits perfectly! This implies x4=256 and y4=81, which means x2=16 and y2=9. Thus, x=±4 and y=±3.
The Geometric Victory
We have found our coordinates. The roots are the four points (4,3),(4,−3),(−4,3), and (−4,−3).
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 x=−4 and x=4, which is 8.
The width, parallel to the imaginary axis, is the distance between y=−3 and y=3, which is 6. The area of a rectangle is simply length times width.
So, 8×6=48. 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.