Question

Answer 1

Answer 2

 Từ gt : \(\dfrac{a}{c}=\dfrac{c}{b}\Rightarrow c^2=ab\)

a) \(\dfrac{a^2+c^2}{b^2+c^2}=\dfrac{a^2+ab}{b^2+ab}=\dfrac{a\left(a+b\right)}{b\left(a+b\right)}\)

\(=\dfrac{a}{b}\left(đpcm\right)\)

b) \(\dfrac{b^2-a^2}{a^2+c^2}=\dfrac{\left(b-a\right)\left(b+a\right)}{a^2+ab}\)

\(=\dfrac{\left(b-a\right)\left(b+a\right)}{a\left(a+b\right)}=\dfrac{b-a}{a}\left(đpcm\right)\)