In an isosceles triangle, the apex angle is 80°, what is the base angle of this isosceles triangle?
等腰三角形中，顶角是80°，这个等腰三角形的底角是多少．
<gadget id="calculator">180 - 80</gadget>
<output>100</output>

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

<result>50</result>