1, the reciprocal formula of exponential formula and logarithmic formula: log_N=b, _ = n (a > 0, a≠ 1, n > 0).

2 、( ab)_=a_b_(a>0，b>0，r∈Q).

3. Double angle formula: tan2a = 2tana/[1-(tana) 2]; cos2a=(cosa)^2-(sina)^2=2(cosa)^2- 1= 1-2(sina)^2； sin2A=2sinA*cosA .

4. General equation of circle: x _+y _+dx+ey+f = 0 (d _+e _-4f > 0).

5. The sum of the probabilities of N mutually exclusive events occurrences is p (a _+a _+a _ ...+a _) = p (a _)+p (a _)+...+p (a _).