考虑从函数的角度理解证：即证 tanx - x - x³/3 > 0 (0 < x < π/2)令 f(x) = tanx - x - x³/3 x∈(0,π/2) 则 f'(x) = sec²x - 1 - x² = tan²x - x²= (tan + x)(tanx - x) 由 tanx +...wonderful\(^O^)/