solve vs thresh out

solve

verb
  • To loosen or separate the parts of. 

  • to find out the perpetrator, the motive etc (of crime) 

  • To algebraically manipulate an equation or inequality into a form that isolates a chosen variable on one side, so that the other side consists of an expression that may be used to generate solutions. 

  • To find an answer or solution to a problem or question; to work out. 

  • To find the values of variables that satisfy a system of equations and/or inequalities. 

thresh out

verb
  • To extract or remove by threshing. 

  • To thrash out. 

How often have the words solve and thresh out occurred in a corpus of books? (source: Google Ngram Viewer )