=1/9 a的6次方b的4次方 ×(-8a³b的6次方)÷(1/81a的8次方b的8次方)
=-72ab²
2、[(x+y)²-(x+y)(x-y)]÷2y
=(x+y)(x+y-x+y)÷2y
=2y(x+y)÷2y
=x+y