we have, z = –9

Let -9 = rcosθ and 0 = rsinθ

By squaring and adding, we get

(-9)² + (0)² = (rcosθ)² + (rsinθ)²

⇒ 81 = r²(cos²θ + sin²θ)

⇒81 = r²

⇒ r = 9

Thus, the required polar form is 9(cos π+i sin π)