There is an isosceles triangle, one of the base angles is 80 degrees, what is the apex angle?
有一个等腰三角形，其中一个底角是80度，它的顶角是多少度．
<gadget id="calculator">80 * 2</gadget>
<output>160</output>

<gadget id="calculator">180 - 160</gadget>
<output>20</output>

<result>20</result>