If the quadratic equation 9x² + 8kx + 16 = 0 has real and equal roots, then the value of k is (A) 3 (B) –3 (C) –4 (D) 3/2

MathsCBSE Class 10 · Standard · Board exam 2026, set 30/4/1 · 1 mark · MCQ

CBSE Class 10 Mathematics Standard 2026: question 1

Set in the CBSE Class 10 board exam of 2026, paper 30/4/1, section A, question 1, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q1 · 1 mark · MCQQuadratic Equations

If the quadratic equation $9 x^{2} + 8 k x + 16 = 0$ has real and equal roots, then the value of k is

(A)3
(B)–3
(C)–4
(D) $\frac{3}{2}$

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 30/4/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Real and equal roots means the discriminant is zero.

Hint 2

Write $b^{2} - 4 a c$ with $b = 8 k$ , $a = 9$ , $c = 16$ .

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

Equal roots $\Rightarrow D = b^{2} - 4 a c = 0$ : $(8 k)^{2} - 4 (9) (16) = 0 \Rightarrow 64 k^{2} = 576 \Rightarrow k^{2} = 9$ .
So $k = \pm 3$ ; both 3 (A) and –3 (B) are listed, so either option is correct.
1 mark

Answer: k = ±3; option (A) 3 (or (B) –3)

Where the marks are

Uses $D = 0$ to get $k = \pm 3$ and chooses (A) or (B) (1 mark)

Revise the chapter

Chapter: Quadratic Equations (notes, formulas, where marks are lost and every past question)
Topic: Nature of Roots and Discriminant

Practise this chapterBoard-style questions from Quadratic Equations, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 30/4/1 (Standard): every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.

CBSE Class 10 Mathematics Standard 2026: question 1

Hints

Step-by-step solution

Revise the chapter

More questions from Quadratic Equations