import graph;
size(4inch);
axes();
real f(real x){
	return 1-x*x;
}

draw(graph(f,-1,1));

draw((.5,0)--(.5,f(.5)));
fill((.5,0)--graph(f,.5,1)--(1,0)--cycle,lightgrey);
label("$x>\frac 12$",(.75,0),S);