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