Answer:
We are multiplying sin theta by sec theta, so we first start with valuing sec theta. Re-evaluate sec theta as sec(theta), and get the reciprocal.
<-- reciprocal
Combine sin() with the reciprocal of sec theta.
Rewrite this combination as tan(theta)
Since the sides are equal, they count as an identity.
That said, sin(theta) × sec(theta) = tan(theta) is an identity.