If the perimeter of an isosceles triangle is 20 cm and one side is 2 cm long, what is the length of its waist in cm?
一个等腰三角形的周长为20cm，且一边长2cm，则它的腰长多少cm．
<gadget id="calculator">20 - 2</gadget>
<output>18</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<result>9</result>