equation vs question

equation

noun
  • The act or process of equating two or more things, or the state of those things being equal (that is, identical). 

  • An assertion that two expressions are equal, expressed by writing the two expressions separated by an equal sign; from which one is to determine a particular quantity. 

  • A small correction to observed values to remove the effects of systematic errors in an observation. 

question

noun
  • A sentence, phrase or word which asks for information, reply or response; an interrogative. 

  • A subject or topic for consideration or investigation. 

  • A proposal to a meeting as a topic for deliberation. 

  • A doubt or challenge about the truth, accuracy, or validity of a matter. 

verb
  • To ask a question or questions; inquire or seek to know; examine. 

  • To ask questions of; to interrogate; to ask for information. 

  • To raise doubts about; have doubts about. 

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