[tex]\it a) \ \ 2mx^2+5mx+6=0\\ \\ -1\in S \Rightarrow 2m\cdot(-1)^2+5m\cdot(-1)+12=0 \Rightarrow 2m-5m+12=0 \Rightarrow \\ \\ \Rightarrow -3m=-12\bigg|_{\cdot(-1)} \Rightarrow 3m=12\bigg|_{:3} \Rightarrow m=4[/tex]
[tex]\it c)\ \ (m+1)x^2+(2m-5)x+26=0\\ \\ 2\in S \Rightarrow (m+1)\cdot4+(2m-5)\cdot2+26=0 \Rightarrow \\ \\ \Rightarrow 4m+4+4m-10+26=0 \Rightarrow 8m+20=0 \Rightarrow 8m=-20\bigg|_{:8} \Rightarrow m=2,5[/tex]
