An isosceles triangle whose apex angle is 20°, find its base angle.
一个等腰三角形，它的顶角是20°，求它的底角．
<gadget id="calculator">180 - 20</gadget>
<output>160</output>

<gadget id="calculator">160 / 2</gadget>
<output>80</output>

<result>80</result>