Given that the base angle of an isosceles triangle is 50°, what is the apex angle of this isosceles triangle?
已知一个等腰三角形的底角是50°，这个等腰三角形的顶角是多少度？
<gadget id="calculator">50 * 2</gadget>
<output>100</output>

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

<result>80</result>