An isosceles triangle whose apex angle is 50°, find its base angle.
一个等腰三角形，它的顶角是50°，求它的底角．
<gadget id="calculator">180 - 50</gadget>
<output>130</output>

<gadget id="calculator">130 / 2</gadget>
<output>65</output>

<result>65</result>