The base angle of an isosceles triangle is 45°, how much is a vertex angle?
等腰三角形中底角45°，一个顶角多少度？
<gadget id="calculator">45 * 2</gadget>
<output>90</output>

<gadget id="calculator">180 - 90</gadget>
<output>90</output>

<result>90</result>