It is difficulf for me to interpret what you want to plot.
One way to 'include' an area of inequality in a plot is to use the patch function. I have done this once here to demonstrate the approach, however you will need to make any necessary corrections to my single patch call, and then add your own for the other conditions.
Try something like this --
clear;clc;close all
%{
x_1 = X
x_2 = Y
x_3 = Z
%}
X = [0:1:400];
Y = [0:1:400];
Z = [0:1:400];
% EQ 1A
cond1 = 2.*X;
%EQ 1B
cond2 = 3.*X;
%EQ 2A
xline(150)
%EQ 2B
xline(280)
cond5 = 173 + Y;
cond6 = 20 + Y;
plot3(X,cond1,Z,'DisplayName',"cond1")
patch([X flip(X)], [zeros(size(cond1)) flip(cond1)], [Z flip(Z)], 'r', DisplayName='cond1 inequality region')
hold on
plot3(X,cond2,Z,'DisplayName',"cond2")
hold on
plot3(X,Y,cond5,'DisplayName',"cond5")
hold on
plot3(X,Y,cond6,'DisplayName',"cond6")
hold on
xline(14)
xline(298)
grid on
grid minor
xlabel("x_1")
ylabel("x_2")
zlabel("x_3")
legend
box on
.
