I looked at the Maple help menu and got acquainted with the op command to extract the elements of a list. How can I extract particular elements of a list. For example....

a:=[2, sqrt(7), "john", sin(57)]

how can I extract elements 2, john and sin(57) ? I tried op( [1,3,4] ,a) but I get an error message.

Thanks in advance!

Sometimes I realize that I need a approximate result rather than an exact answer after I enter Maple command. Is there a way to apply the evalf command at the very end of an input? Thanks in advance!!

How can I permentlly change 2D Math characteristics. (input font and size) ? Thanks!!

I used Maple 12 to calculate the volume of a shpere of radius r by using Integration technique. when I entered the first expression, Maple 12 returns the expression as it is. When I enter a different expression for the same problem I get an exact answer. This has happened before...I am not sure what's going on....

I use two different maple commands but I get the same graph. I am not sure why. I am new to Maple. Thanks in advance. The two commands are:

plot( {2-x^2,x^2},x=-1..1)    and,

plot( [2-x^2,x^2],x=-1..1)

Please let me know.