An isosceles triangle has a base of 12 cm and a perimeter of 52 cm. What is the length of the waist of this triangle?
一个等腰三角形的底边为12厘米，周长为52厘米．这个三角形的腰长多少厘米？
<gadget id="calculator">52 - 12</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>