令x=1998则a=x²+x²(x+1)²+(x+1)²=[(x+1)²-2x(x+1)+x²]+2x(x+1)+x²(x+1)²=(x+1-x)²+2x(x+1)+x²(x+1)²=1²+2x(x+1)+x²(x+1)²=[1+x(x+1)]²...