As others have said, GPL license isn't allowed in PEAR. I would suggest LGPL or BSD.
The packaging needs to be addressed (the tgz you supplied isn't a PEAR package tarball) but this can obviously be dealt with once the package is accepted.
Please remove the .class from the filenames.
get_class() isn't the right way to check for the right object type. It precludes extension. Please use is_a() instead.
And also CS issues (yes, they're important).
return should not have parenthesis (it is a language construct, not a function).
equalsSum() should return/raise an error if the wrong # of arguments is passed in instead of returning and doing nothing. Same for equalsDifference(), etc.
"and" should be &&, "or" should be ||.
"else" should always be on the same line as }. (You use 3 different styles in different places).
Not conditions, just requests:
Support for variabel other than 'x' would be nice (and fairly easily implemented I would think), although if it slows things down I can understand not implementing it for now.
I would appreciate it if you would change your strings from using " to using '. Since you do no variable interpolation ' is more appropriate (see previous threads on the pear lists for more).
I know quite a bit about polynomials but wasn't able to really dig into your algorithms. The examples seem to run ok, so I think the code should be good.