If a cylinder is shortened by 5 cm, the surface area will be reduced by 78.5 cm2. What is the radius of the base of the cylinder in cm?
把一个圆柱截短5厘米，表面积就减少78.5平方厘米，这个圆柱的底面半径是多少厘米．
<gadget id="calculator">78.5 / 5 / 3.14 / 2</gadget>
<output>2.5</output>

<result>2.5</result>