5A-3B-[5A-(A+2B)]
=5A-3B-5A+(A+2B)
=-3B+A+2B
=A-B
=(4x^2-1/3x+1)-(3x^2+2/3x-4)
=4x^2-1/3x+1-3x^2-2/3x+4
=x^2-x+5