Different display results to watch out for

with(plots):
a:=x^4-2*x^3+2:
b:=plot(a)
c:=plot(a,filled=true,transparency=0.8)

display(b,c,view=[-1..2,0..5])

Maple takes the default range and zooms in which is why we see the jagged results.  You must include numpoints in your plot options to increase the smoothness, not exactly the best option in this case.

If you include the range in only one plot using display for both plots, it results in a defaulted range if view is not specified.

a:=x^4-2*x^3+2:
b:=plot(a,x=-1..2)
c:=plot(a,filled=true,transparency=0.8)

display(b,c)

If we specify a view range in display, you notice the jagged edge of the graph whose range in the plot was not specified.

b:=plot(a,x=-1..2)
c:=plot(a,filled=true,transparency=0.8)

display(b,c,view=[-1..2,0..5])

Or

b:=plot(a)
c:=plot(a,x=-1..2,filled=true,transparency=0.8)

display(b,c,view=[-1..2,0..5])

It is best just to include the range in all plots to avoid poor graph displays. 

b:=plot(a,x=-1..2)
c:=plot(a,x=-1..2,filled=true,transparency=0.8)
display(b,c)