求助PREP-IR 关于球的计算

sie05

an architect is planning to incorporate several stone spheres of different sizes into the landscaping of a public park,and workers who will be applying a finish to the exterior of the spheres need to know the surface area of each sphere. the finishing process costs $92 per square meter. the surface area of a sphere is equal to 4Pi* r*2,where r is the radius of the sphere. which is the cloest to the cost of finishing a sphere with a  5.5-meter circumference as well as the the cost of finishing a sphere with a 7.85-meter circumference .
我的计算r=5.5/2*pi, s =4*pi* (r的平方），结果为1973，但是答案900，
那位大牛看一下错在哪里了

jojomigi

我照你的方程式算出来886.3，你自己再算一下呢，没看出来有什么问题

rainforest

900正确。楼主可能过程中分母上的2漏掉了平方，差了一倍。