1, square difference formula: a? -B? =(a+b)(a-b)；

2. Calculation of arc length: l = nπ r/180;

3. Complete cubic summation formula: (a? +b？ )=a？ +3a？ b+3ab？ +b？ ;

4, triangle height = area × 2 bottom;

5. Triangle inequality: | a |≤ b