cho a/b = c/d . CM : a) a/a-b = c/c-d b/) a/b =a+c/b+d c)a/3a+b = c/3c+d

0 bình luận về “cho a/b = c/d . CM : a) a/a-b = c/c-d b/) a/b =a+c/b+d c)a/3a+b = c/3c+d”

1. Giải thích các bước giải:

   a.Ta có:
   $\dfrac{a}{b}=\dfrac{c}{d}$

   $\to \dfrac{b}a=\dfrac{d}c$

   $\to 1-\dfrac{b}a=1-\dfrac{d}c$
   $\to\dfrac{a-b}{a}=\dfrac{c-d}{c}$

   $\to\dfrac{a}{a-b}=\dfrac{c}{c-d}$

   b.Ta có:

   $\dfrac{a}{b}=\dfrac{c}{d}=\dfrac{a+c}{b+d}$

   $\to \dfrac{a}{b}=\dfrac{a+c}{b+d}$

    c.Ta có:

   $\dfrac{a}{b}=\dfrac{c}{d}=k$

   $\to a=bk, c=dk$

   $\to\begin{cases} \dfrac{a}{3a+b}=\dfrac{bk}{3bk+b}=\dfrac{k}{3k+1}\\ \dfrac{c}{3c+d}=\dfrac{dk}{3dk+d}=\dfrac{k}{3k+1}\end{cases}$

   $\to \dfrac{a}{3a+b}=\dfrac{c}{3c+d}$

        

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