The perimeter of an isosceles triangle is 39 cm. Its base is 12 centimeters long, how many centimeters is its waist long? (solution by equation)
一个等腰三角形的周长是39厘米．它的底边长12厘米，一条腰长多少厘米？(用方程解)
<gadget id="calculator">39 - 12</gadget>
<output>27</output>

<gadget id="calculator">27 / 2</gadget>
<output>27/2 = around 13.5</output>

<result>27/2 = around 13.5</result>