Solve() command with trigonometric equations

[CyberAngel]

(03-27-2020 10:33 AM)Jan 11 Wrote:  The "solve" command solves any system of equations (trigonometric, polynomial, exponential, square root, various). There is only one remark that you should remember and use. If the system of equations has many solutions, you must provide the approximate solution search area (lower bound, upper bound). I solved this system of trigonometric equations using this principle. The calculator has found many solutions for me, according to my wishes. Fantastic. See this in the attached screenshot from my HP PRIME. Good luck.

I'm using derivative (f'=0) to see the monotonic areas [a, b] where to search the roots with different sign at the ends of the areas. These two together ensure
only one root in the area.