A sheet of tin is cut so as to form a circular ring that has an a_英语解答

A sheet of tin is cut so as to form a circular ring that has an area of 18 square inches.The total outer and inner perimeters of the ring measure 36 inches.Find the inner radii and the outer radii of the ring.Use area of circle=派r^ circumference=2派r and 派=3.14.Give the answer to three significant figures

人气：159 ℃　时间：2020-05-30 10:11:03

解答

pi*(r1^2-r2^2)=18 and 2*pi*(r1+r2)=36,第一个公式按平方差展开,再代入第二个公式,可以得到r1=r2+1,代回第二个公式可得：r1=(19+pi)/2pi,r2=(19-pi)/2pipi是什么意思pi是圆周率啊，不知道符号怎么打。就是题干中的“派”