One base angle of an isosceles triangle is 75°, what is its top angle?
等腰三角形的一个底角是75°，它的顶角是多少度？
<gadget id="calculator">75 * 2</gadget>
<output>150</output>

<gadget id="calculator">180 - 150</gadget>
<output>30</output>

<result>30</result>