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For which value of is NOT a quadratic equation?

Class 10Quadratic EquationsAlgebra — Quadratics
  • A
  • B
  • C
  • D

Step-by-Step Solution

An equation is quadratic only when the coefficient of is non-zero. Here , so exactly when , and the equation collapses to the linear . At the coefficient is −3, at it is −6 and at it is −1 — all non-zero, so all three still give genuine quadratic equations.
Answer: B)

Key idea: Method 2: Completing the square

Rewrite into the form .

**Steps for **:
1. Take half the coefficient of .
2. Square it: .
3. Add and subtract this value to complete the perfect square.

Example: .
→
→
→ ±2 → or −5.

Completing the square is how the quadratic formula is DERIVED. It's slower than factorisation but works ALWAYS (no clever guessing required).

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