In a right triangle, the ratio of the degrees of the two acute angles is 4:5, what is the degree of the smaller acute angle?
一个直角三角形，两个锐角的度数比为4：5，较小的一个锐角多少°度．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">90 * (4/9)</gadget>
<output>40</output>

<result>40</result>