添加辅助线就可以了,以H点为FC线段做垂直线
设长是a 宽是b阴影面积(0.5a+AH)xb÷2-AHx0.5b÷2+HDx0.5b÷2=0.25ab+0.5AHxb-0.25ahxb+0.25 HDxb=0.25ab+0.25AHxb+0.25HDxb=0.25ab+(0.25AH+0.25)xb=0.25ab+0.25ab=0.5ab=0.5x48=24平方厘米