解得3/8
2/5÷﹙﹣12/5﹚-8/21×﹙﹣7/4﹚-1/2÷2×1/2
=﹣1/6-﹙﹣2/3﹚-1/8
=﹣1/6+2/3-1/8
=1/2-1/8
=3/8
PS:如果能帮助你的话,希望能采纳哦!