Código LaTeX usando pacotes tikz plotando gráfico com funções admissiveis

funcoes_admissiveis.tex

%
% Código LaTeX usando pacotes tikz plotando gráfico com funções admissiveis
% Por Eduardo Oliveira (https://eduardojm.github.io)
%
\documentclass{standalone}

\usepackage{tikz}
\usepackage{tkz-fct}

\begin{document}

	\begin{tikzpicture}
		\tkzInit[xmin=-1, xmax=6, ymin=-1, ymax=6]
		% draw axis without ticks
		\tkzDrawX[noticks]
		\tkzDrawY[noticks]
		
		% define extrems on y(x) curve
		\tkzDefPoint[](2.5, 2.0){A}
		\tkzDefPoint[](4.6, 3.76){B}		
		% define helper points
		\tkzDefPoint[](2.5, 0.0){C}
		\tkzDefPoint[](4.6, 0.0){D}
		\tkzDefPoint[](0.0, 2.0){E}
		\tkzDefPoint[](0.0, 3.76){F}
		% helper points to put labels
		\tkzDefPoint[](3.4, 3.2){G}
		\tkzDefPoint[](2.6, 1.7){H}
		\tkzDefPoint[](3.7, 4.2){I}
		\tkzDefPoint[](3.2, 0.4){J}
		
		% draw extrem points on y(x) curve
		\tkzDrawPoint[fill=black, size=7](A)
		\tkzDrawPoint[fill=black, size=7](B)
		
		% y(x)
		\tkzFct[domain=2.5:4.6]{-exp(-x+3.2)+4}
		% eta(x)
		\tkzFct[domain=2.5:4.6]{-0.18*x*x+1.29*x-2.09}
		% y(x) + 2*eta(x)
		\tkzFct[domain=2.5:4.6,dashed]{-exp(-x+3.2)+4+2*(-0.18*x*x+1.29*x-2.09)}
		% y(x) - 4*eta(x)
		\tkzFct[domain=2.5:4.6,dashed]{-exp(-x+3.2)+4-4*(-0.18*x*x+1.29*x-2.09)}
		
		% draw dotted segments (x_1, y_1), (x_2, y_2)
		\tkzDrawSegment[dotted](A,C)
		\tkzDrawSegment[dotted](B,D)
		\tkzDrawSegment[dotted](A,E)
		\tkzDrawSegment[dotted](B,F)
		
		% x_1, x_2, y_1, y_2 labels
		\tkzLabelPoint[below](C){$x_1$}
		\tkzLabelPoint[below](D){$x_2$}
		\tkzLabelPoint[left](E){$y_1$}
		\tkzLabelPoint[left](F){$y_2$}
		
		\tkzLabelPoint[right](G){$y(x)$}
		\tkzLabelPoint[right](H){$Y_2(x)=y(x)+\varepsilon _2 \eta(x)$}
		\tkzLabelPoint[right](I){$Y_1(x)=y(x)+\varepsilon _1 \eta(x)$}
		\tkzLabelPoint[right](J){$\eta(x)$}
	\end{tikzpicture}
	
\end{document}