二分之一m-【n-二分之五m-2(3m-2n)

问题描述:

二分之一m-【n-二分之五m-2(3m-2n)

1/2m-[n-5/2m-2(3m-2n)]
=1/2m-n+5/2m+2(3m-2n)
=3m-n+6m-4n
=9m-5n