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Mathematics — CBSE Class 10 board question

Q1. [1]
Which of the following is a quadratic polynomial having zeroes $\dfrac{-2}{3}$ and $\dfrac{2}{3}$ ?
  1. A $4x^2 - 9$
  2. B $\dfrac{4}{9}(9x^2 + 4)$
  3. C $x^2 + \dfrac{9}{4}$
  4. D $5(9x^2 - 4)$
Previously asked in CBSE board exam
2023 30/1/1 Q14
Generated by claude-sonnet-4-6 · 2026-06-15 10:36 · grounding rag
Model Answer

Answer: D

$5(9x^2 - 4) = 5(3x-2)(3x+2)$, giving zeroes $x = \dfrac{2}{3}$ and $x = -\dfrac{2}{3}$. ✓

Source: Chapter 2, Section 2.3

Explanation

To find the correct option, check which polynomial gives zeroes $\frac{2}{3}$ and $-\frac{2}{3}$. The required polynomial is of the form $k(x - \frac{2}{3})(x + \frac{2}{3}) = k(x^2 - \frac{4}{9})$. Option D: $5(9x^2 - 4) = 45(x^2 - \frac{4}{9})$, which matches. Option A ($4x^2 - 9$) gives zeroes $\pm\frac{3}{2}$, not $\pm\frac{2}{3}$. Always substitute the zeroes or factorise to verify quickly.

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