Sigma Percentile
JEE Main 2024 (05 Apr Shift 2)
LEVELJEE Main

Animated Solution for Mathematics - Functions: Let be defined as : and . Then the function is

Select Answer:

Visualized Solution

Defining the Composite Function

  • Let
  • Substitute into
  • Result:

Setup for

  • For ,
  • Substitute:

Simplifying for

  • Since
  • Therefore,
  • Modulus opens positively:

Setup for

  • For ,
  • Substitute:
  • Simplifies to:

Simplifying for

  • Since , the modulus opens negatively.
  • Result:

The Final Piecewise Function

Injectivity (One-One) Test

  • A function is one-one if
  • We use the Horizontal Line Test.

Applying Horizontal Line Test

  • A horizontal line (for ) intersects the curve twice.
  • Example: and
  • Since , it is not one-one.

Surjectivity (Onto) Test

  • A function is onto if Range = Codomain.
  • Given Codomain =

Finding the Range

  • From the graph, the minimum value is at .
  • The graph extends upwards to infinity.
  • Range =

Final Conclusion

  • Since Range , it is not onto.
  • Final Result: The function is neither one-one nor onto.

The Sigma Insight: Classification of Functions

Solution Diagram

Analyzing the Setup

Welcome, fellow traveler, to the beautiful world of composite functions! Today, we are going to dissect a problem that perfectly illustrates how functions interact.
We are given and a piecewise function . Our goal is to understand the nature of .
Think of as a two-stage machine: first, the input passes through the machine, and then the output of that machine is fed into the machine.

The Two-Stage Transformation

Our master equation is . Because is defined differently for positive and negative inputs, our composite function must also be defined piecewise.
Let us look at the case where . Here, . Substituting this into our master equation, we get:
Now, consider the behavior of for . Since , the expression is always non-negative.
Thus, the modulus simply vanishes, leaving us with . This is the right branch of our function, starting from the origin and climbing rapidly toward infinity.

The Left-Hand Side

Now, let us shift our focus to the region where . In this domain, .
Substituting this into , we get:
The and cancel out, leaving us with . Since we are in the domain , the definition of the modulus tells us that .
So, for the left side, our function is simply the line . This is a straight line descending from infinity to the origin.

The Final Verdict

We have now constructed our function:
If you visualize this, you see a V-shaped curve that touches the origin.
Now, let us test for injectivity (one-one). If we draw a horizontal line at , it intersects the graph at two points: one on the left branch and one on the right. Because a horizontal line hits the graph twice, the function is not one-one.
Finally, let us test for surjectivity (onto). The graph starts at and goes up to infinity. It never touches the negative -axis.
Since the Range is $

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