Generally, the equations of linear function and quadratic function are 0, 1,-1, 2, -2.

For fractional functions, generally take 0 (to ensure that the denominator is not zero), 1,-1 and 1/2,-1/2, etc. , and try to appear as an integer;

For trigonometric functions, those are special values, such as plus or minus ninety degrees, sixty degrees, zero degrees;

For logarithmic functions, the power of e, 1, e is generally taken, even 1/e,1/(e k) and so on.

For exponential function, it is easy to get, how to get it conveniently;

For functions with parameters, generally, except 0, 1 and-1, select values related to parameters, such as ax+3(a is non-zero) and x= 1/a, so as to eliminate parameters. Of course, there are more complicated ones that need to be observed by yourself.