The sum of the apex and base angles of an isosceles triangle is 100°, what is the apex angle in degrees?
一等腰三角形的顶角和底角的和是100°，它的顶角是多少度．
<gadget id="calculator">180 - 100</gadget>
<output>80</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<result>20</result>