It is known that a base angle of an isosceles triangle is 50°, what is the apex angle of it?
已知等腰三角形的一个底角是50°，它的顶角是多少°．
<gadget id="calculator">50 * 2</gadget>
<output>100</output>

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

<result>80</result>