The radius of the base of a cylinder is 5cm and the height is 4cm. What is its lateral area in cm**2.
一个圆柱的底面半径是5cm，高是4cm，它的侧面积是多少cm**2．
<gadget id="calculator">2 * 3.14 * 5 * 4</gadget>
<output>125.6</output>

<result>125.6</result>