In the Desmos app, using degrees, the derivative of tan is not equal to sec^2(x). Instead sec^2(x)*pi/180 matches d/dx tan(x). In short sec^2(x) is broken.

Hi there! Typically, for calculator-related bug reports I’d recommend emailing support@desmos.com — In this case, though, there’s a quick answer: the derivative of `tan(x)`

is only equal to `sec(x)^2`

when working in radians! You can find a fuller discussion on this stackexchange post: integration - Why do we require radians in calculus? - Mathematics Stack Exchange