Cut the largest triangle out of a trapezoid whose upper base is 5 cm, lower base is 15 cm, and height is 5 cm. Find the area of the triangle.
在一块上底是5厘米，下底是15厘米，高是5厘米的梯形里剪最大的三角形，求三角形的面积是多少．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">15 * (5/2)</gadget>
<output>75/2 = around 37.5</output>

<result>75/2 = around 37.5</result>