A×B=1
C+D=0
M=-1
M÷[A×﹙B+C+D﹚]÷2×M
=-1÷[A×B+A×﹙C+D﹚]÷2×﹙-1﹚
=-1÷﹙1+A×0﹚÷2×﹙-1﹚
=﹣1÷1÷2×﹙﹣1﹚
=﹣1/2×﹙﹣1﹚
=1/2