-1/2+1/2÷[(-3/2)³+(-1/2)}×|-2.5²|-1/2
=-1/2+1/2÷[-27/8+(-1/2)}×|-2.5²|-1/2
=-1/2+1/2÷(-31/8)×|-2.5²|-1/2
=-1/2-4/31×25/4-1/2
=-1-25/31
=-1又25/31