"Create Functions in terms of X1"

NSolve[2X1+X2-2X1(X1+X2)==0,{X2}]
NSolve[3X1+X2-0.5(3+2Sqrt[2])==0,{X2}]

g1=2X1(X1-1)/(1-2*X1)
g2=2.91421-3X1

Plot[{g1,g2},{X1,0.5,1.0},PlotRange->{{.7,1.0},{0.,1.0}}]
Show[%,Frame->True,GridLines->Automatic]