If one base angle of an isosceles triangle is 20°, what is the apex angle?
等腰三角形的一个底角是20°，那么顶角是多少°
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">180 - 40</gadget>
<output>140</output>

<result>140</result>