Analyzing the Setup
Welcome, fellow traveler on the path to JEE excellence. Today, we are not just solving an integral; we are uncovering a hidden symmetry.
When you first look at the expression
I=∫616logex2+loge(x2−44x+484)logex2dx
it might seem intimidating. It looks like a complex mess of logarithms and quadratics, but in the world of competitive mathematics, complexity is often just a mask for elegance.
The Hidden Identity
Let us look at the denominator. Specifically, focus your attention on the quadratic expression x2−44x+484.
If you have been practicing your algebraic identities, you might notice that 484 is the square of 22, and 44 is exactly 2×22. This is the classic expansion of (x−22)2.
By recognizing this, we transform our integral into:
I=∫616logex2+loge(x−22)2logex2dx
The King's Property
The King's Property states that for any continuous function f(x) on the interval [a,b], the integral ∫abf(x)dx is equal to ∫abf(a+b−x)dx.
Here, our limits are 6 and 16. Their sum is 22. This is not a coincidence; it is a mathematical invitation.
By replacing x with (22−x), we are essentially looking at the function from the other side of the mirror. Let us perform the substitution:
I=∫616loge(22−x)2+loge((22−x)−22)2loge(22−x)2dx
Look closely at the second term in the denominator. The expression ((22−x)−22)2 simplifies beautifully to (−x)2, which is just x2.
Our new integral is:
I=∫616loge(22−x)2+logex2loge(22−x)2dx
The Grand Cancellation
Now, we have two versions of I. If we add them together, something magical happens.
The denominators are identical, and the numerators add up to the exact same expression as the denominator:
2I=∫616logex2+loge(22−x)2logex2+loge(22−x)2dx
Because the numerator and denominator are now the same, the entire integrand collapses into 1. We are left with the simplest integral imaginable:
Evaluating this is straightforward:
Therefore, the final result is:
I=5
Final Reflections
We started with a complex logarithmic expression, and through the power of symmetry and the King's Property, we reduced it to a simple subtraction. This is the beauty of JEE mathematics.
It is not about brute force; it is about finding the right perspective. Whenever you face a difficult integral, pause, look for the symmetry, and look for the perfect squares. The answer is often hiding in plain sight, waiting for you to apply the right property.