Question: Graph problem - string of number instead of graph

Hi everyone,

i plotted a graph last time, and Maple showed a very clear graph. But when i Opened my file on the next day agian and re-enter t to my input. Maple gave me a string of number instead of graph. Even to teacher's guide as well, sometime Maple gives nicely graph, but mostly a string of number. Can anyone give me solution ? Thx a lot

My graph:

pic:=plot([2*cos(x),exp(x)], x=-3..3,y=-5..5):
t1:=textplot([1.4,2.3,"y =exp(x)"]):
t2:=textplot([3,-2.4,"y=2cos(x)"]):

display(pic,t1,t2);
display(INTERFACE_PLOT(CURVES([[-3., -1.97998499320089084], [-2.86921707499999990, -1.92626907202658359], [-2.75542355124999982, -1.85271746466719000], [-2.62745083250000011, -1.74143016958698716], [-2.49862982749999984, -1.60064570741438650], [-2.37042108624999992, -1.43418921559316081], .........
........

My teacher guide graph:

pic:=plot([x^2, -x^2, x^2 * sin(x)], x=0..2*Pi, thickness=[0,0,2]):
t1:=textplot([5.5,35,"x^2"]):
t2:=textplot([5.5,-35,"-x^2"]):
t3:=textplot([5.5,-10,"x^2 sin(x)"]):
display(pic,t1,t2,t3);