Question

giúp mik

giúp mik với 

Answer 1

\(a,-\left(m+n-k\right)+\left(m-k\right)-\left(-m+n\right)\\ =-m-n+k+m-k+m-n\\ =\left(-m+m+m\right)+\left(-n-n\right)+\left(k-k\right)\\ =m-2n\)

\(b,\left(x-y\right)-\left(x+y\right)-\left(2x-3y\right)\\ =x-y-x-y-2x+3y\\ =\left(x-x-2x\right)+\left(-y-y+3y\right)\\ =-2x+y\)