Question 6 - CBSE Class 10 Sample Paper for 2026 Boards - Maths Standard [Term I] - Solutions of Sample Papers for Class 10 Boards

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Question 6 Which one of the following is not a quadratic equation? (A) (𝑥 + 2)2 = 2(𝑥 + 3) (B) 𝑥2 + 3𝑥 = (-1)(1 – 3𝑥)2 (C) 𝑥3 – 𝑥2 + 2𝑥 + 1 = (𝑥 + 1)3 (D) (𝑥 + 2)(𝑥 + 1) = 𝑥2 + 2𝑥 + 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 + 9x2 term, so it will be a quadratic equation Option (c) will have x3 term cancelled out, and will have –x2 term on right, and 3x2 term on the left, so it will be a quadratic equation Option (d) will have x2 term cancelled out, so it will be not be a quadratic equation Thus, instead of checking each option, let’s just check Option (d) first Checking Option (D) Simplifying (𝑥 + 2)(𝑥 + 1) = 𝑥2 + 2𝑥 + 3 x(𝑥 + 1) + 2(𝑥 + 1) = 𝑥2 + 2𝑥 + 3 x2 + x + 2x + 1 = 𝑥2 + 2𝑥 + 3 x2 + 3x + 1 = 𝑥2 + 2𝑥 + 3 x2 + 3x + 1 – (𝑥2 + 2𝑥 + 3) = 0 x2 + 3x + 1 – 𝑥2 – 2𝑥 – 3 = 0 x2 – 𝑥2 + 3x – 2𝑥 + 1 – 3 = 0 x – 2 = 0 Since this is not of the form ax2 + bx + c = 0 Hence, it is not a quadratic equation So, correct answer is (d)