csc^2(u) - cos(u)sec(u) = cot^2(u)

Use the same process as I described in repsonse to your other post: https://www.askmehelpdesk.com/mathematics/verify-trigonometry-identity-744696.html

Figured it out :)

csc^2x = 1 + cot^2x

and since -cosxsecx = -1

1 + cot^2x - 1 = cot^2x

Identity verified :)