（6xy+5x)÷x
=x×(6y+5)÷x
=6y+5
(8a²b-4ab²）÷4ab
=4ab×(2a-b)÷4ab
=2a-b
(15x²y-10xy²）÷5xy
=5xy×(3x-2y)÷5xy
=3x-2y
(4c²d+c³d³）÷（-2c²d)
=c²d×(4+cd²)÷(-2)÷c²d
=(4+cd²)×(-1/2)
=-(4+cd²)/2