a^2*b=2
(-1/3)*a*b(a+a^3*b-a^5*b^2)
=(-1/3)*a*b*a(1+a^2*b-a^4*b^2)
=(-1/3)*a^2*b[1+a^2*b(1-a^2*b))]
=(-1/3)*2*[1+2(1-2)]
=(-2/3)*[1-2]
=2/3
a^2*b=2
(-1/3)*a*b(a+a^3*b-a^5*b^2)
=(-1/3)*a*b*a(1+a^2*b-a^4*b^2)
=(-1/3)*a^2*b[1+a^2*b(1-a^2*b))]
=(-1/3)*2*[1+2(1-2)]
=(-2/3)*[1-2]
=2/3