嘗試使用求解方程時遇到問題sympy。一些變量已分配了特定的值。我試圖求解方程b，c和d。這是我的嘗試：from random import randintimport sympyfrom sympy.abc import b,c,d,B,C,r,xB=10C=20r=123# Equation: x^3+b*x^2+c*x+d=x^3+(B?r)x^2+(C?B*r)x?C*requation = sympy.Eq(x**3+b*x**2+c*x+d,x**3+(B?r)*x**2+(C?B*r)*x?C*r)print(sympy.solve(equation,"b"))print(sympy.solve(equation,"c"))    print(sympy.solve(equation,"d"))Python向我顯示以下錯誤：    [user@user Python Scripts]$ python polygen.py   File "polygen.py", line 10    equation = sympy.Eq(x**3+b*x**2+c*x+d,x**3+(B?r)*x**2+(C?B*r)*x?C*r)                                                  ^SyntaxError: invalid character in identifier我想念什么？