Sigma Percentile
JEE Main 2020 (9 January Shift 2)
LEVELJEE Main

Animated Solution for Mathematics - Sets and Relations: If and then :

Select Answer:

Visualized Solution

The Number Line Canvas

  • We need to find the sets and on the real number line.
  • Visualizing intervals helps prevent errors in intersections and unions.

Decoding Set

  • Set
  • Recall the property:

Interval for Set

  • Applying the property:
  • In interval notation:

Decoding Set

  • Set
  • Recall:

Splitting the Inequality

  • Case 1:
  • Case 2:

Interval for Set

  • From Case 1:
  • From Case 2:

Finding

  • Let's check Option 4:
  • Look at the overlap between Set and Set .

Evaluating

  • Overlap is from (open) to (closed).
  • Option 4 is incorrect.

Finding

  • Let's check Option 2:
  • means elements in but NOT in .

Evaluating

  • Remove the overlap from .
  • Left part becomes .
  • Right part is untouched.

Final Conclusion

  • This is exactly all real numbers except the interval .
  • Option 2 is correct!

The Sigma Insight: Types of Sets and Set Operations

Solution Diagram

Analyzing the Setup

The real number line represents an infinite road stretching from to . Our objective is to define two sets, and , and determine the result of the set difference .

Decoding Set

The Neighborhood
Set is defined by the inequality . Geometrically, represents the distance of a point from the origin .
The condition identifies all points whose distance from the origin is strictly less than . This creates a symmetric open interval centered at .

Decoding Set

The Repulsion
Set is defined by the inequality . This implies that the distance of from the point must be at least .
This condition splits into two distinct linear inequalities: 1. 2.
Thus, the set consists of two rays:

The Surgical Strike:

The operation requires us to take the set and remove any elements that are also contained within set . We must identify the overlap between and .
The ray overlaps with in the interval . Removing this overlap from the ray leaves us with the interval .
The second part of , which is , shares no common elements with . Therefore, this portion remains entirely unchanged.

Final Calculation

By combining the remaining segments, we arrive at the final set:
This result represents all real numbers except those in the open interval . We can express this elegantly as:
The final result is $(-\infty, -2] \cup

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