Answer
$(90- x)^{\circ}$
$ \sin x^{\circ} = \cos ( 90- x)^{\circ}$
Work Step by Step
$ \sin x^{\circ} = \cos ( 90- x)^{\circ}$
Reason-
sine and cosine are cofunctions and
$ x^{\circ} + (90-x)^{\circ} = 90^{\circ}$
i.e. $ x^{\circ}$ and $ (90-x)^{\circ}$ are complementary angles.
