A(2;2); B(m+3;4)
=>\(\overrightarrow{AB}=\left(m+3-2;4-2\right)\)
=>\(\overrightarrow{AB}=\left(m+1;2\right)\)
A(2;2); C(m+1;5)
=>\(\overrightarrow{AC}=\left(m+1-2;5-2\right)\)
=>\(\overrightarrow{AC}=\left(m-1;3\right)\)
Để A,B,C thẳng hàng thì \(\dfrac{m+1}{m-1}=\dfrac{2}{3}\)
=>3m+3=2m-2
=>m=-5