> f4:= x -> 9 - x^2;

> g4:= x -> sqrt(9-x);

> a4:= plot(f4(x), x = -3..3, thickness=2, color = black):

> b4:= plot(g4(x), x = 0..9, thickness=2, color = red):

> c4:= plot(x, x = 0..9, thickness=2, color = blue):

> d4:= textplot([2.3,7,`f4`], thickness=2, color = magenta):

> e4:= textplot([6,5,`y=x`], thickness=2, color = magenta):

> h4:= textplot([5,1.5,`g4`], thickness=2, color = magenta):

> display({a4,b4,c4,d4,e4,h4});