Which pair of equations can be used to verify the rectangular form, z = a + bi, and the polar form of a complex number are equivalent?

The polar form is z = r(cos θ + i sin θ). Distributing r gives z = r cos θ + i(r sin θ). Matching this with the rectangular form z = a + bi shows that a = r cos θ and b = r sin θ, which is choice D.

AI-written and checked against the verified answer.