6а+7b/a - 5a/42b, если а/b=14

Question

6а+7b/a - 5a/42b, если а/b=14

Answer 1

7b=-6a: b=-6a/7.
(5a+3(-6a/7))/(4a+5(-6a/7))=(5a-18a/7)/(4a-30a/7)=
(35a-18a)/(28a-30a)=17a/(-2a)=-8,5.