7a-9b+(a+b) 6.6x-2 2/7y-(0.06x-3 5/7y) --c)) : ) желательно показать всё: ) : )

1. 7a-9b+(a+b)=7a-9b+a+b=7a+a-9b+b=8a-8b=8(a-b)
3/ c-((d-l)-(a-c))=c-(d-l-a+c)=c-d+l+a-c=-d+l+a
2/ 6x-2 2/7y - (0.06x-3 5/7y)= 6x-16/7y-(0.06x-26/7y)=6x-16/7y-0.06x+26/7y=6x-0.06x-16/7y+26/7y=5.94x+10/7y