JEE 2022 — Mathematics PYQ
JEE | Mathematics | 2022For real number a, b (a > b > 0), let: Area {(x,y):x2+y2≤a2 and a2x2+b2y2≥1}=30π Area {(x,y):x2+y2≥b2 and a2x2+b2y2≤1}=18π Then the value of (a−b)2 is equal to ________.
Choose the correct answer:
- A.
12
(Correct Answer) - B.
13
- C.
14
- D.
15
12
Explanation
Solution
1. Understand the Areas
-
Total Circle Area: πa2
-
Total Ellipse Area: πab
-
Total Smaller Circle Area: πb2
2. Formulate Equations
The first area is the Circle minus the Ellipse (where they overlap): πa2−πab=30π⟹a2−ab=30.
The second area is the Ellipse minus the small Circle: πab−πb2=18π⟹ab−b2=18.
3. Solve for a and b
Adding the two equations: a2−b2=48⟹(a−b)(a+b)=48.
Subtracting the second from the first: a2−2ab+b2=30−18=12.
The expression a2−2ab+b2 is exactly (a−b)2.
Result: 12.
Explanation
Solution
1. Understand the Areas
-
Total Circle Area: πa2
-
Total Ellipse Area: πab
-
Total Smaller Circle Area: πb2
2. Formulate Equations
The first area is the Circle minus the Ellipse (where they overlap): πa2−πab=30π⟹a2−ab=30.
The second area is the Ellipse minus the small Circle: πab−πb2=18π⟹ab−b2=18.
3. Solve for a and b
Adding the two equations: a2−b2=48⟹(a−b)(a+b)=48.
Subtracting the second from the first: a2−2ab+b2=30−18=12.
The expression a2−2ab+b2 is exactly (a−b)2.
Result: 12.

