Question 4 - CBSE Class 10 Sample Paper for 2026 Boards - Maths Basic - Solutions of Sample Papers for Class 10 Boards

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Question 4 Which of the following is not a quadratic equation? (A) (𝒙 + 2)2 = 2(𝒙 + 3) (B) 𝒙2 + 3𝒙 = (−1)(1 − 3𝒙2 ) (C) (𝒙 + 2)(𝒙 − 1) = 𝒙2 − 𝟐𝒙 − 3 (D) 𝒙3 − 𝒙2 + 2𝒙 + 1 = (𝒙 + 1)3To check if quadratic equation, we simplify the equations and represent it in the form ax2 + bx + c = 0 Where a ≠0 By guessing, we notice that Option (a) will have x2 term, so it will be a quadratic equation Option (b) will have x2 term on left side and +3x2 on right side, so it will be a quadratic equation Option (c) will have x2 term on left side and x2 on right side, which will cancel out. So, it may not be a quadratic equation Option (d) will have x3 term on left side and x3 on right side, which will cancel out. And, it will have –x2 term on left side and +3x2 on right side, so it will be a quadratic equation Thus, instead of checking each option, let’s just check Option (c) first Checking Option (C) Simplifying (𝑥 + 2)(𝑥 – 1) = 𝑥2 – 2𝑥 – 3 x(𝑥 – 1) + 2(𝑥 – 1) = 𝑥2 – 2𝑥 – 3 x2 – x + 2x – 2 = 𝑥2 – 2𝑥 – 3 x2 + x – 2 = 𝑥2 – 2𝑥 – 3 x2 + x – 2 – (𝑥2 – 2𝑥 – 3) = 0 x2 + x – 2 – 𝑥2 + 2𝑥 + 3 = 0 x2 – 𝑥2 + x + 2𝑥 – 2+ 3 = 0 3x + 1 = 0 Since this is not of the form ax2 + bx + c = 0 Hence, it is not a quadratic equation So, correct answer is (c)