Sigma Percentile
JEE Advanced 2012
LEVELJEE Main

Animated Solution for Mathematics - Quadratic Equations: The value of is

Enter Numerical Value:

Visualized Solution

Identify the Nested Structure

  • Given expression:
  • Focus on the infinite nested radical part.

Define a Variable for the Infinite Part

  • Let

Form the Recursive Equation

  • Since the pattern is infinite, the nested part inside the first square root is exactly .
  • Equation:

Remove the Square Root

  • Square both sides of the equation.

Convert to Standard Quadratic Form

  • Multiply the entire equation by to clear the denominator.
  • Rearrange:

Identify Coefficients and Discriminant

  • Compare with .
  • , ,
  • Discriminant

Calculate the Discriminant

Find the Roots

  • Using the quadratic formula:

Select the Valid Root

  • Two possible values: or
  • Since is a principal square root, .
  • Therefore,

Substitute Back into the Main Expression

  • Original expression:
  • Substitute :

Simplify the Argument of the Logarithm

  • Multiply the fractions:
  • Denominator:
  • Argument becomes:

Express as a Power of the Base

  • We need to evaluate
  • Notice that
  • To match the base , invert the fraction:

Final Calculation

  • Final value:
  • Key Takeaway: Infinite nested radicals can be solved by identifying the self-similar recursive part and forming a quadratic equation.

The Sigma Insight: Solution of Quadratic Equations

The Infinite Puzzle

A Journey into Nested Radicals
Have you ever looked at a problem and felt like it was staring back at you, daring you to blink? This problem is exactly that—a beautiful, intimidating, infinite nested radical wrapped in a logarithm.
It looks like a labyrinth, but I promise you, there is a clear path through it. Let's walk this path together.

Phase 1

The Infinite Sea
Look closely at the expression:
It is easy to get lost in the dots, but the secret to solving infinite structures is to find the self-similarity. Imagine you are standing on the edge of this infinite sequence; if you were to peel away the very first layer, you would see the exact same infinite pattern staring back at you.
Let's define this entire repeating nested radical as a single variable, :
Because the pattern is infinite, we can replace the inner repeating part with itself. This transforms our terrifying infinite expression into a simple, elegant recursive equation:

Phase 2

The Quadratic Transformation
Now that we have our equation, we need to strip away that square root. Squaring both sides gives:
To make this look like a standard quadratic equation, let's clear the denominator by multiplying the entire equation by :
Rearranging everything to one side, we arrive at:
This is a standard quadratic equation of the form , where , , and .

Phase 3

The Discriminant & The Choice
Let's calculate the discriminant, . Substituting our values:
Calculating this carefully:
Since is a perfect square (), we use the quadratic formula to find:
This gives us two potential values for : or .
Because is defined as a principal square root, it must be non-negative. We reject the negative root and accept:

Phase 4

The Logarithmic Finale
We are almost there. Let's substitute back into our original expression:
Simplifying the argument, the numerator is and the denominator is . Thus, the argument is .
Now we evaluate the logarithm:
Finally, we add the from the beginning:
The complexity collapses, the infinite sequence resolves, and we are left with a clean, satisfying integer. The final answer is 4.

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