填空题 .For each of the following functions, give the domain and a description of the graph y=f(x) in the xy-plane, including its shape, and the x- and y- intercepts.

填空题 16.  f(x)=-4

填空题 17.  f(x)=100-900x

填空题 18.  f(x)=5-(x+20)2

填空题 19. 

填空题 20.  f(x)=x+|x|