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Choose the correct value of $(\sec A+\tan A)(1-\sin A)$.
A$\sec A$
B$\sin A$
C$\csc A$
D$\cos A$
Answer & Solution
Correct answer: D. $\cos A$
Rewrite in terms of sine and cosine: $(\frac{1}{\cos A}+\frac{\sin A}{\cos A})(1-\sin A)=\frac{1+\sin A}{\cos A}(1-\sin A)$. This becomes $\frac{1-\sin^2 A}{\cos A}=\frac{\cos^2 A}{\cos A}=\cos A$.
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