2兀R+2兀xR/2+2兀R四分之一
=2兀R(1+1/2+1/4)
=2兀R(4/4+2/4+1/4)
=2兀R×(7/4)
=7兀R/2
实际上:2兀R+2兀xR/2+2兀R四分之一等于:二分之七×兀R.
答案:2分之5x兀R有误!