9.982²=(10-0.018)²=10²-2×10×0.018+0.018²=100-0.36+0.000324=99.640324x+1/x=3 两边平方x²+2×x×1/x+1/x²=9x²+2+1/x²=9x²+1/x²=9-2=7x²+1/x²=7 ...