2ab[3/4a^(m+1)-1/2b^m]-[2/3a^(m+1)-5/6b^m]*3ab
=3/2a^(m+2)b-ab^(m+1)-2a^(m+2)b+5/2ab^(m+1)
=3/2ab^(m+1)-1/2a^(m+2)b
=1/2ab[3b^m-a^(m+1)]