Introduction to Trigonometry
RD Sharma
CBSE
Grade 10
Question:
The value of $(\sec A + \tan A)(1 - \sin A)$ is:
(a) $\cos A$
(b) $\sin A$
(c) $\sec A$
(d) $\csc A$
Step-by-Step Solution
Key Concept: $\left(\dfrac{1 + \sin A}{\cos A}\right)(1 - \sin A) = \dfrac{1 - \sin^2 A}{\cos A} = \dfrac{\cos^2 A}{\cos A} = \cos A$.
$\dfrac{1 - \sin^2 A}{\cos A} = \dfrac{\cos^2 A}{\cos A} = \cos A$. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Simplifying to $\cos A$: 1.0 Mark
Correct Answer: $\cos A$
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