If the base angle of an isosceles triangle is 40 degrees, what is the apex angle of the isosceles triangle?
一个等腰三角形的底角是40度，那么这个等腰三角形的顶角是多少度．
<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">180 - 80</gadget>
<output>100</output>

<result>100</result>