If the base angle of an isosceles triangle is 45°, what is the apex angle?
如果一个等腰三角形底角是45°，它的顶角是多少．
<gadget id="calculator">45 * 2</gadget>
<output>90</output>

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

<result>90</result>