We now consider an inequality of the formf1（x）>f2（x）.Every numerical value x0 taken from the domain ofadmissible values is called a solution of theinequality,if,when x0 is substituted into both sidesof the inequality,the result is a true numericalinequality.All the solutions of an inequalityconstitute the solution set of the inequality.Forinstance,the inequality x2<1 has for its solution setthe open interval（-1,1）.Sometimes,for the sakeof brevity,we loosely say that the solution of
Certain elementary notions of geometry,such asthe point,the straight line,and the plane,cannot bedefined with the aid of other still more elementaryconcepts and they serve as the starting point in anyexposition of geometry.Usually,points are denoted by capital lettersA,B,C,...,and straight lines by small letters a,
The set of real numbers has the property of be-ing ordered:for any numbers a and b we have oneand only one of the these relations:a>b(a is greaterthan b),a=b,or ab means the difference a-b is positive;thenotation ab and c>d are said to
If A and B are two sets,A is said to be a subsetof B if and only if every element of A is also anelement of B.The subset relation is indicated by thesymbolismAB(or BA)which is read"A is a subset of B"or"A is includedin B"or"B includes A".It is clear from the definition that every set A isa subset of itself.It is important to know that theempty setis the subset of any set A:A.(Wewill explain it in the logic part)Two sets A and B are said to be equal if
