x=var('x')
n=var('n')
n=8
f=sqrt(x)
p1=plot(f,(x,0,4))
for i in range(0,n,1):p1+=polygon([(i/2,0), (i/2+4/n,0), (i/2+4/n,f(i/2+4/n)), (i/2,f(i/2+4/n))], rgbcolor=(1/8,3/4,1/2))
aa=var('aa')
xi=var('xi')
aa=0
xi=0
for j in range (0,8,1):xi=xi+4/n; aa=aa+f(xi)*4/n
print "aa= %s" %N(aa,digits=4)
ae=integral(f(x), x, 0, 4)
print "ae= %s" %N(ae, digits=4)
print " %s percent" %N((aa-ae)/ae *100, digits=2)
p1