500(1+x)+500(1+x)(1+x) = 1997-342-500
(1+x)+(1+x)(1+x) = (1997-342-500)/500
1+x+1+2x+x² = 1155/500
x²+3x+2 = 2.31
x²+3x-0.31 = 0
(x+3.1)(x-0.1) = 0
可得：x1 = -3.1 ,x2 = 0.1 .