Someproblemsaredifficulttosolve.Buttherearealotofnumber...
问题详情：Someproblemsaredifficulttosolve.Buttherearealotofnumberexpressionsthatcanhelp.Forexample,ifweputtwoandtwotogether,wemightcomeupwithrightanswer.Weknowthattwoheadsarebetterthanone,Itisalwaysbett...