Solve nonlinear differential equation system - Plot

When I solve the system of differential equations I get two solutions for each variable (See the picture). My question is how I can neglect one of the solutions at the plot. Thanks.

Code:

[![\text{Plot}\left$\text{Evaluate}\left$$\left\{\sqrt{y(x)},z(x)\right\}\text{/.}\, \%\right$,\{x,0,60\},\text{PlotRange}\to \text{All},\text{PlotPoints}\to 200\right$$ \left(\text{sol}=\text{NDSolve}\left$\left\{3 y(x)-0.5 z(x)^2=y(x) (9 \eta y(x)+0.5) z'(x)^2\text{/.}\, \eta \to 1,-y'(x)=-\eta y(x) y'(x) z'(x)^2+(4 \alpha +18) \eta y(x)^2 z'(x)^2+y(x) z'(x)^2\text{/.}\, \{\eta \to 1,\alpha \to 1\},y(0)=1,z(0)=0.2\right\},\{z,y\},\{x,0,60\}\right$\right)]]

• Replace the % with sol[] to take the first part? Hard to check without code that can be copied. – Chris K Nov 14 '18 at 3:10
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