If the apex angle of an isosceles triangle is 80 degrees, what is the base angle?
等腰三角形的顶角是80度，它的底角是多少度．
<gadget id="calculator">180 - 80</gadget>
<output>100</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<result>50</result>