y=(m-1)x+m
=>(m-1)x-y+m
\(d\left(O;d\right)=\dfrac{\left|\left(m-1\right)\cdot0+\left(-1\right)\cdot0+m\right|}{\sqrt{\left(m-1\right)^2+1}}=\dfrac{\left|m\right|}{\sqrt{\left(m-1\right)^2+1}}\)
Để d(O;d) bé nhấtthì \(\sqrt{\left(m-1\right)^2+1}_{min}\)
=>m-1=0
=>m=1