In an isosceles triangle, the ratio of the vertex angle to the base angle is 5:2, what is the vertex angle of this isosceles triangle?
一个等腰三角形，它的顶角和一个底角数的比是5：2，这个等腰三角形的顶角是多少度．
<gadget id="calculator">5 + 2 + 2</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>