Use two identical isosceles right triangles to form a square. Given that the perimeter of a square is 20 centimeters, what is the area of an isosceles right triangle in square centimeters?
用两个完全相同的等腰直角三角形拼成一个正方形．已知正方形的周长是20厘米，一个等腰直角三角形的面积是多少平方厘米．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">5 * (5/2)</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>