Q. If a + b = 10 and ab = 21, then the value of (a - b)2 is
A) 16
B) 15
C) 18
D) 17
✔ Correct Answer: 16
Exam Insight
We know that (a + b)² = a² + b² + 2ab. Substituting the given values, 10² = a² + b² + 2(21). Solving, 100 = a² + b² + 42, so a² + b² = 58.