[ot][ot][ot][personal] whirligig small thoughts

[Undescribed Horrific Abuse, One Victim & Survivor of Many]

so removing the parts that started turning into volume without
integration, there's:

triangle_area = 1/2 r_slice^2 dtheta
r_slice = sqrt(r_sphere^2 - x^2)

then we can write wedge volume
wedge_volume = integral(triangle_area, x=-r_sphere..+r_sphere)