manuilovaan

Ответ:

1)a-2a+3ab-5a-7ab= -6a-4ab= -2a•(3+2b)

2) -2ab+4xy+2ab+5xy=4xy+5xy=9xy

3) 7ab+4xy -(5ab-9xy)=2ab+4xy+9xy=2ab+13xy