Giải các phương trình sau : ( biến đổi đặc biệt )
a) \(\frac{x+1}{65}\) + \(\frac{x+3}{63}\)= \(\frac{x+5}{61}\)+ \(\frac{x+7}{59}\)
b) \(\frac{x+29}{31}\)- \(\frac{x+27}{33}\)= \(\frac{x+17}{43}\)- \(\frac{x+15}{45}\)
c) \(\frac{x+6}{1999}\)+ \(\frac{x+8}{1997}\)= \(\frac{x+10}{1995}\)+ \(\frac{x+12}{1993}\)
d) \(\frac{1909-x}{91}\)+ \(\frac{1907-x}{93}\)+ \(\frac{1905-x}{95}\)+ \(\frac{1903-x}{91}\)+ 4 = 0