How do you express the complex number in trigonometric form 2(cos 180° + i sin 180°)?

The trigonometric form of a complex number $a + b i$ is $r \left(\cos \theta + i \sin \theta\right)$ where $r = \sqrt{{a}^{2} + {b}^{2}}$ and $\theta$ satisfies $\theta = \arccos a \text{/"r,theta=arcsin b"/} r$