@vv  Hi，sorry again. what if I changed the question that b is column 7 from A and matrix C that is made from columns 1 to 6 and 8 to 11 of A, when I solved for x, I typed exactly u post, but there is an error says "first matrix deminsion (10) second matrix deminsion (7); How can I deal with this...and why it works for my question?

Cheers.

@Preben Alsholm  Alright, thanks for your helping.

@Kitonum  I got your idea. But can u explain to me how to use implicitplot in Maple. Thanks a lot. 

@Preben Alsholm  Alright, thanks mate

@Kitonum  Alright, thanks mate

@Kitonum  Alright. Thanks mate.

@vv Alright! Thanks mate.

@vv  I mean.. can u show me the whole process, there are few things hard to understand...

@vv sorry, I don't understand...

@Carl Love  I did exactly what u typed in, but the Maple says there is an error.  In your first step, there are serval answers,but when I typed argument(%); it says expecting get 1 , but got 5. It's really confused .. could u pls explain to me ?

Cheers. 

@Kitonum  Ummmm... But the answer is a constant number mutiply by Pi ..I really confused about the Pi...I tried serval times, the answer still Float (infinity)..OMG

@Kitonum  Oh, I got it. Thanks mate!