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For the expression $\sqrt{1-x^2}$, a useful trigonometric substitution is
A$x=\tan\theta$
B$x=\sec\theta$
C$x=\sin\theta$
D$x=\csc\theta$
Answer & Solution
Correct answer: C. $x=\sin\theta$
If $x=\sin\theta$, then $1-x^2=1-\sin^2\theta=\cos^2\theta$, so $\sqrt{1-x^2}$ simplifies neatly. This is the standard substitution for this form.
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