The length of the base of an isosceles triangle is 5 cm and the length of the waist is 8 cm. What is its perimeter in cm?
等腰三角形中底边的长度是5厘米，腰的长度是8厘米，它的周长是多少厘米．
<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">5 + 16</gadget>
<output>21</output>

<result>21</result>