Polar & rectangular forms of complex numbers

Given a complex number in rectangular form, write it in polar form. Given a complex number in polar form, write it in rectangular form.

Problem

Express z, start subscript, 1, end subscript, equals, 10, open bracket, cosine, left parenthesis, 270, degree, right parenthesis, plus, i, sine, left parenthesis, 270, degree, right parenthesis, close bracket in rectangular form.
Express your answer in exact terms.
z, start subscript, 1, end subscript, equals