FromPolarCoordinates

FromPolarCoordinates[{r,θ}] gives the {x,y} Cartesian coordinates corresponding to the polar coordinates {r,θ}. 

FromPolarCoordinates[{r,θ1,…,θn-2,ϕ}] gives the coordinates corresponding to the hyperspherical coordinates {r,θ1,…,θn-2,ϕ} 

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