https://mapleprimes.com/questions/224329-Why-Does-Solve-Drop-Solutions-To-This
Why does solve drop solutions to this trig function? - MaplePrimes
trig functionsolvedropsolutions
https://www.dummies.com/article/academics-the-arts/math/trigonometry/determine-domain-and-range-in-a-trig-function-149455/
Determine Domain and Range in a Trig Function | dummies
domain and rangetrig functiondeterminedummies