1, the circumference of a circle = pi× diameter = pi× radius× 2c = π dc = 2π r;

2. The law of multiplicative association: (ab) c = a (BC);

3. Trapezoidal area = (upper bottom+lower bottom) × height ÷ 2s = (a+b) h ÷ 2;

4. The surface area of a cuboid = (length× width+length× height+width× height )× 2s = 2 (AB+AH+BH);

5. One person's speed = meeting distance ÷ meeting time-the speed of another person.