NDA 2026 · PYQ · Quadratic Equations · hard
If the highest degree coefficient is equal to 1, then what is the total number of quadratic equations which are unchanged on squaring their roots?
Answer
The correct answer is B: 4. Let roots be α, β. After squaring, roots are α², β².
- A.6
- B.4✓ Correct
- C.2
- D.None
Let roots be α, β. After squaring, roots are α², β². For unchanged equation, {α, β} = {α², β²}. Cases: (i) α = α², β = β² gives α, β ∈ {0, 1}, yielding pairs (0,0), (0,1), (1,1) — three equations: x², x(x−1), (x−1)². (ii) α = β², β = α² with α ≠ α²: α = α⁴ gives α³ = 1, α ≠ 1, so α is a primitive cube root of unity. This gives one equation x² + x + 1 = 0. Total = 3 + 1 = 4.
💡
Practice unlimited NDA PYQs + AI-tracked progress on each topic.
Sign up free →More Quadratic Equations questions
Want more NDA practice?
Free daily 10-Q quiz · adaptive mocks · 49,000+ practice questions (19,000+ verified PYQs) · AI doubt solver in Hindi + English