Check if $(2,\pi/2)$ lies on $r=2\cos(2\theta)$ 

Plugging $\theta=\pi/2$ gives $r=-2$  

Plugging $r=2$ gives $\cos(2\theta)=1\Rightarrow \theta=n\pi$  

However the [graph](https://www.desmos.com/calculator/we712du0qd) shows the point lies on the graph. I know this has to do with multiple representations of the same point, but couldn't proceed further. Any help?