The lengths of the two sides of a right triangle are two prime numbers and their sum is 12. Find the area of this triangle.
一个直角三角形的两条直角边的边长是两个质数，和是12．求这个三角形的面积．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 5 * 7</gadget>
<output>35/2 = around 17.5</output>

<result>35/2 = around 17.5</result>