10.28.3 Can you answer these questions?

10.28.3.1 Getting conditions for existence of trigonometric solutions

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=306363

Consider the following problem. Define a trigonometric function f(x): 
 f[x_]:=a*Sin[2*x]+b*Cos[2*x]+c*Cos[x]+d*Sin[x]-e 
 
We want a range of $x$ for which $f(x)\leq 0$... 
[equation-solving] [inequalities]
 

asked by Shoham Sen https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=79641 Score of 1

answered by user64494 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=7152 Score of 0

10.28.3.2 How to use the tedious definitional results to make a next definition for FindRoot?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=306376

I am trying to use a designed function to find the quasi-normal modes. 
... 
[functions] [function-construction] [evaluation] [programming] [syntax]
 

asked by Robert Xu https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=30993 Score of 1

10.28.3.3 Why does EstimatedProcess (via TimeSereisModelFit) give a different result for the same data than LinearModelFit?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=306433

This is a question about Mathematica's behavior.  I give some background -- but you can skip to the code block below, which illustrates the behavior. 
I am using Mathematica ("WL") to work ... 
[time-series]
 

asked by Tom Barson https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=84497 Score of 1