[tex]\it \overrightarrow{u}=(m+1)\overrightarrow{i}+4\overrightarrow{j}\\ \\ \overrightarrow{v}= 2\overrightarrow{i}+(m-1)\overrightarrow{j}\\ \\ \overrightarrow{u},\ \ \overrightarrow{v}\ \ coliniari\ \Rightarrow \dfrac{m+1}{2}=\dfrac{4}{m-1} \Rightarrow (m-1)(m+1)=2\cdot4 \Rightarrow\\ \\ \Rightarrow m^2-1=8|_{+1} \Rightarrow m^2=9 \Rightarrow \sqrt{m^2}=\sqrt9 \Rightarrow |m|=3 \Rightarrow m=\pm3[/tex]
