What are the outstanding characteristics of elementary mathematics compared with later mathematics? Introduction to the history of elementary mathematics, the period of elementary mathematics lasted more than two thousand years from the fifth century BC to the seventeenth century AD, and ended with the establishment of advanced mathematics. The most obvious achievement in this period is the systematic establishment of elementary mathematics, that is, arithmetic, elementary algebra, elementary geometry (plane geometry and solid geometry) and plane triangle in the current primary and secondary school curriculum. The period of elementary mathematics can be divided into two parts according to different contents, namely, the period of geometric development (to the second century AD) and the period of algebraic priority development (from the second century AD to the seventeenth century AD). It can also be divided into "Greek period", "Oriental period" and "European Renaissance period" according to different historical conditions. The Greek period coincided with the general prosperity of Greek culture. Greece is an ancient civilization, but compared with Babylon, Egypt, India and China, Greek civilization is a little later in the history of civilization. Greek civilization lasted 1000 years; According to the development of mathematics, it can be divided into classical period and Alexander period. Oriental period mainly refers to the decline of ancient Greece, the development center of western mathematics moved eastward to India; Arabia, etc. The Renaissance in Europe is a period when elementary mathematics developed to a certain stage, preparing for the development of mathematics to a higher stage.

It is known that in △ABC, be and cf are bisectors of ∠B and ∠C, and be = cf Proof: AB=AC.

As soon as the proof method is set with AB≠AC, it is better to set AB & gtAC, so ∠ ACB >; ∠ABC, so ∠ BCF =∠ FCE =∠ ACB/2 > ∠ ABC/2 =∠ CBE =∠ EBF.

In △BCF and △CBE, because BC=BC, BE=CF, ∠ BCF >; ∠CBE。

So Chief Executive BF>. (1)

As a parallelogram BEGF, then ∠EBF=∠FGC, EG=BF, FG=BE=CF, and even CG.

So △FCG is an isosceles triangle, so ∠FCG=∠FGC.

Because ∠FCE & gt；; ∠FGE, so ∠ ECG