Using the trigonometric identity \( \sin \theta = \cos(90^\circ - \theta) \), we have:
\[
\sin 42^\circ = \cos(90^\circ - 42^\circ) = \cos 48^\circ
\]
Thus, the expression simplifies to:
\[
\frac{\sin 42^\circ}{\cos 48^\circ} = \frac{\cos 48^\circ}{\cos 48^\circ} = 1
\]
Therefore, the correct answer is 1.