`b)[5(x-y)^n+2(x-y)^(n+2)-7(x-y)^(n+1)]:[1/2 (x-y)^(n-1)] (n in NN^(**))`

`=5(x-y)^n :[1/2 (x-y)^(n-1)]+2(x-y)^(n+2) :[1/2 (x-y)^(n-1)]-7(x-y)^(n+1) :[1/2 (x-y)^(n-1)]`

`=(5: 1/2).(x-y)^(n-(n-1))+(2: 1/2).(x-y)^((n+2)-(n-1))-(7: 1/2).(x-y)^((n+1)-(n-1))`

`=10(x-y)^1+4(x-y)^3 -14(x-y)^2`

`=4(x-y)^3-14(x-y)^2+10(x-y)^1`