# source("http://macosa.dima.unige.it/r.R")
dev.new(width=8, height=4); rowcol(1,2)
a=0; b=15; c=0; d=50; a1=a; b1=b; c1=0; d1=250; x1=3; x2=5; x3=10
h = function(x) ifelse(x < 3,10,ifelse(x < 5,10+20*(x-3),ifelse(x < 10,50-10*(x-5),0)))
k = function(t) integral(h, 0,t)
Box_(a,b, c,d); GRAPH2(h, a,x1, "black"); type(2.5,45,"F")
Box_(a1,b1, c1,d1); type(2.5,225,"area")
for(x in seq(a,x1,0.05)) Dot2(x,integral(h, a,x),"seagreen")
wait(3)
Box_(a,b, c,d); GRAPH2(h, a,x2, "black"); type(2.5,45,"F")
Box_(a1,b1, c1,d1); type(2.5,225,"area")
for(x in seq(a,x2,0.05)) Dot2(x,integral(h, a,x),"seagreen")
wait(3)
Box_(a,b, c,d); GRAPH2(h, a,x3, "black"); type(2.5,45,"F")
Box_(a1,b1, c1,d1); type(2.5,225,"area")
for(x in seq(a,x3,0.05)) Dot2(x,integral(h, a,x),"seagreen")
wait(3)
Box_(a,b, c,d); GRAPH2(h, a,b, "black"); type(2.5,45,"F")
Box_(a1,b1, c1,d1); type(2.5,225,"area")
for(x in seq(a,b,0.05)) Dot2(x,integralB(h, a,x),"seagreen")
# for "integralB" see here)

      

# Or (in 2 windows):
graphics.off()  # <- if you want shut down all open graphics devices
a=0; b=15; c=0; d=50; a1=a; b1=b; c1=0; d1=250; x1=3; x2=5; x3=10
A=10; D=A+305
h = function(x) ifelse(x < 3,10,ifelse(x < 5,10+20*(x-3),ifelse(x < 10,50-10*(x-5),0)))
k = function(t) integral(h, 0,t)
P = function(x) dev.set(dev.prev()); R = function(x) replayPlot(x); S = function(x) recordPlot()
dev.new(width=3, height=3, xpos=A, ypos=A); Box_(a,b, c,d); type(2.5,45,"F"); fig01 = S()
dev.new(width=3, height=3, xpos=D, ypos=A); Box_(a1,b1, c1,d1); type(2.5,225,"area"); fig02 = S()
P(); R(fig01); for(x in seq(a,x1,0.05)) Dot2(x,h(x),"black"); fig01=S()
P(); R(fig02); for(x in seq(a,x1,0.05)) Dot2(x,integral(h, a,x),"seagreen"); fig02=S()
wait(2)
P(); R(fig01); for(x in seq(x1,x2,0.025)) Dot2(x,h(x),"black"); fig01=S()
P(); R(fig02); for(x in seq(x1,x2,0.05)) Dot2(x,integral(h, a,x),"seagreen"); fig02=S()
wait(2)
P(); R(fig01); for(x in seq(x2,x3,0.05)) Dot2(x,h(x),"black"); fig01=S()
P(); R(fig02); for(x in seq(x2,x3,0.05)) Dot2(x,integral(h, a,x),"seagreen"); fig02=S()
wait(2)
P(); R(fig01); for(x in seq(x3,b,0.05)) Dot2(x,h(x),"black"); fig01=S()
P(); R(fig02); for(x in seq(x3,b,0.05)) Dot2(x,integralB(h, a,x),"seagreen")
## dev.set(dev.prev()) returns the previous device