They are not second - order approximations, but are exact for any amount of deformation.它们不是二次近似, 而是对任何变形量都成立的精确表达式.We do not have the true figures so we will have to make some approximations.我们没有真实的数字，因此只能作些粗略的估计。There ...
Such estimates should be considered only as crude approximations.上述估算结果只能是粗略的近似值.There are two approaches generally used to arrive at these approximations.通常有两种方法用于获得近似解析式.They are not second - order approximations, but ...