Question

Ta có: a/b = c/d

CMR: 3a - 4b/b = 3c - 4d/d

4 cách

Answer 1

Đặt \(\dfrac{a}{b}=\dfrac{c}{d}=k\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=bk\\c=dk\end{matrix}\right.\)

Ta có: \(\dfrac{3a-4b}{b}=\dfrac{3\cdot bk-4b}{b}=3k-4\)

\(\dfrac{3c-4d}{d}=\dfrac{3dk-4d}{d}=3k-4\)

Do đó: \(\dfrac{3a-4b}{b}=\dfrac{3c-4d}{d}\)