Function diagram: the arc segment is shaped like a function of ∨, such as y = x 2.
Convex function: Let the function f(x) be defined on [a, b]. X2 is true if there are any two differences in [a, b] x 1: f [(x 1+x2)/2].
Function diagram: the arc segment is shaped like a function of ∩, such as y =-x 2.
F(x)=lgx is a convex function. From the function image, the quadratic function with downward opening is convex and the quadratic function with upward opening is concave.