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Introduction to Trigonometry
CBSE 2026 Board Exam Set 3 (Code 30/1/3)
CBSE_BOARD_PYQ_2026_30_1_3
Grade 10
Question:
[Section A]
If $\sin \theta = \dfrac{a}{b}$, then $\cos \theta$ is equal to:
(a) $\dfrac{b}{\sqrt{b^2-a^2}}$
(b) $\dfrac{b}{a}$
(c) $\dfrac{\sqrt{b^2-a^2}}{b}$
(d) $\dfrac{a}{\sqrt{b^2-a^2}}$
If $\sin \theta = \dfrac{a}{b}$, then $\cos \theta$ is equal to:
(a) $\dfrac{b}{\sqrt{b^2-a^2}}$
(b) $\dfrac{b}{a}$
(c) $\dfrac{\sqrt{b^2-a^2}}{b}$
(d) $\dfrac{a}{\sqrt{b^2-a^2}}$
Step-by-Step Solution
Key Concept: $\cos \theta = \sqrt{1 - \sin^2 \theta} = \sqrt{1 - \dfrac{a^2}{b^2}} = \dfrac{\sqrt{b^2-a^2}}{b}$.
$\cos \theta = \sqrt{1 - \dfrac{a^2}{b^2}} = \dfrac{\sqrt{b^2-a^2}}{b}$. [1.0 Mark]
Correct Answer: (c) $\dfrac{\sqrt{b^2-a^2}}{b}$
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