Question: confusing output

Question:confusing output

kpassi 208 Maple

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....

When I enter 2*int(Pi(r^2 - y^2),y=0..r)     I get int(Pi(r^-y^2)dy) ....(the output int is given as the Integral sign by Maple). Basically Maple is saying the it can't solve the problem by giving me the origional problem back.

When I enter ....

radius:=sqrt(r^2-y^2):

2*int(Pi radius^2,y=0..r) I get the exact expression for the volume of a sphere : (4/3) Pi r^3

 

Any clarifitcation will be greatly appreciated. Thanks!!!

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