Assertion (A): For θ = 1, θ must be 0. Reason (R): ²θ - ²θ = 1. Select the correct answer from the codes below. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

MathsCBSE Class 10 · Basic · Board exam 2026, set 430/3/1 · 1 mark · Assertion-reason

CBSE Class 10 Mathematics Basic 2026: question 19

Set in the CBSE Class 10 board exam of 2026, paper 430/3/1, section A, question 19, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q19 · 1 mark · Assertion-reasonCompetency-basedIntroduction to Trigonometry

Assertion (A): For $sin θ = 1$ , $cos θ$ must be 0.

Reason (R): $sin^{2} θ - cos^{2} θ = 1$ .

Select the correct answer from the codes below.

(A)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(B)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
(C)Assertion (A) is true, but Reason (R) is false.
(D)Assertion (A) is false, but Reason (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 430/3/1.

Hints

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

Hint 1

Use the fundamental identity to test A.

Hint 2

Try $θ = 0^{\circ}$ in R.

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.

From $sin^{2} θ + cos^{2} θ = 1$ : $1 + cos^{2} θ = 1 \Rightarrow cos θ = 0$ . A is true.
½ mark
R is false: e.g. $θ = 0^{\circ}$ gives $0 - 1 = - 1 \neq = 1$ . The correct identity is $sin^{2} θ + cos^{2} θ = 1$ .
½ mark

Answer: Option (C)

Where the marks are

Shows A true (½ mark)
Shows R false by counter-example (½ mark)

Revise the chapter

Chapter: Introduction to Trigonometry (notes, formulas, where marks are lost and every past question)
Topic: Proving Simple Trigonometric Identities

Practise this chapterBoard-style questions from Introduction to Trigonometry, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 430/3/1 (Basic): 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 Basic 2026: question 19

Hints

Step-by-step solution

Revise the chapter

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