The ratio of the base angle to the apex angle of an isosceles triangle is 2:5, what is the apex angle of this triangle?
等腰三角形的底角和顶角度数的比是2：5，这个三角形的顶角是多少度．
<gadget id="calculator">2 + 2 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">180 * (5/9)</gadget>
<output>100</output>

<result>100</result>