Cho 1/c=1/2 (1/a+1/b) ( vs a,b,c ≠0, b≠c). CMR a/b=a-c/c-b Giúp mk vs, hết điểm r

$\dfrac1c =\dfrac12\left(\dfrac1a +\dfrac1b\right)$

$\to \dfrac1c =\dfrac{a+b}{2ab}$

$\to 2ab = c(a+b)$

$\to ab – ac = bc – ab$

$\to a(b-c) = b(c-a)$

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

$\to \dfrac ab =\dfrac{a – c}{c -b}$ (đpcm)