Question

Tính A= -a+b-1 biết \(\frac{3a+7b}{7a+3b}\)=1

Answer 1

\(\frac{3a+7b}{7a+3b}=1\)

\(\Rightarrow\)3a+7b=7a+3b

\(\Rightarrow\)7b-3b=7a-3a(chuyển vế đổi dấu)

\(\Rightarrow\)4b=4a

\(\Rightarrow\)b=a

\(\Rightarrow\)b-a=0

hay -a+b=0

\(\Rightarrow\)-a+b-1=0-1= -1

Hay A= -1

Tik mik nha!

Answer 2

Ta có:

\(\frac{3a+7b}{7a+3b}=1\\ \Rightarrow3a+7b=7a+3b\\ \Rightarrow7b-3b=7a-3a\\ \Rightarrow4b=4a\\ \Rightarrow a=b\\ \)

Thay \(a=b\) vào \(A=-a+b-1\), ta có:

\(A=-a+a-1\\ \Rightarrow A=0-1\\ A=-1\)

Vậy A=-1