a <- floor(runif(1)*11-5); f <- function(x) (x-a)^2
h <- floor(runif(1)*3)+1; k <- h+floor(runif(1)*2)+1
par( mai = c(0.5,0.5,0.1,0.1) ); plot(f,a-6,a+6, ylim=c(-5,26))
colora <- function(x1,x2,x3,x4) polygon( c(seq(x1,x2,len=100),seq(x3,x4,len=100)),
                     f(c(seq(x1,x2,len=100),seq(x3,x4,len=100))), col="yellow")
colora(-h+a,-k+a,k+a,h+a); abline(h=0,v=0, lwd=3, col="red")
abline(v=seq(-6+a,6+a,1),h=seq(-6,27,1),lty=3,col="grey60")
abline(h=axTicks(2),v=axTicks(1),lty=3); curve(f,add=TRUE,lwd=3)
abline(h=f(h+a),col="blue"); abline(h=f(k+a),col="blue")
lines(c(-k+a,-h+a),c(0,0),lwd=5,col="blue")
lines(c(k+a,h+a),c(0,0),lwd=5,col="blue")
F <- recordPlot(); dev.off(dev.list())
s <- function() { replayPlot(F); cat(-k+a,'<=x<=',-h+a,' o ',h+a,'<=x<=',k+a,"\n")}
cat('risolvi ',f(h+a),'<= ( x -',a,')^2  <=', f(k+a),' Controlla battendo  s()',"\n")