The rectangular coordinates of a point: rectangular

The rectangular_coordinates command finds the rectangular coordinates of a point given its polar coordinates.

rectangular_coordinates takes two arguments:
r, θ, two real numbers.
rectangular_coordinates(r,θ) returns a list of the rectangular coordinates of the point with polar coordinates r and θ.

Example.
Input:

rectangular_coordinates(2, pi/4)

or:

rectangular_coordinates(polar_point(2, pi/4))

Output:

⎡
⎢
⎢
⎣

√

⎤
⎥
⎥
⎦