Shade the region between the lines and xy axis

Hi! I am trying to shade the region I coloured in, but I can't figure it out! help!

My code for the graph:

clear all

x=linspace(-2,8);

y1=(8-2*x);

plot(x,y1)

hold on

y3= (5+2.5*x);

plot(x,y3)

y4=(0*x);

plot(x,y4)

y5=xline(0)

grid on

box on

hold off

Answer 1

[Star Strider]

Try this:

x=linspace(-2,8);
y1=@(x)(8-2*x);
y3= @(x)(5+2.5*x);
y4=@(x)(0*x);
y5=xline(0);
y1_xint = fzero(@(x) y1(x), 1);
y1y3_int = fzero(@(x) y1(x) - y3(x), 1);


figure
plot(x,y1(x))
hold on
plot(x,y3(x))
plot(x,y4(x))
patch([0 y1y3_int y1y3_int 0], [0 0 y3(y1y3_int)  y3(0)],'g', 'EdgeColor','g')
patch([y1y3_int y1_xint [0 0]+y1y3_int], [0 0 y3(y1y3_int)  y3(0)],'g', 'EdgeColor','g')
grid on
box on
hold off

producing:

I created anonymous functions from the line expressions, since that makes the calculations easier. The fzero calls calculate the line intercepts and the ‘y1’ intercept with the x-axis. The area is filled using two patch calls, one for each segment of the area. You can see the segments by removing the 'EdgeColor' arguments and their paired values.

EDIT — (22 Feb 2021 at 20:42)

Another approach using logical vectors and comparisons —

figure
plot(x,y1(x))
hold on
plot(x,y3(x))
plot(x,y4(x))
Lv = x>=0 & x<=y1_xint;
fill([x(Lv) fliplr(x(Lv))], [min(y1(x(Lv)),y3(x(Lv))) zeros(size(x(Lv)))], 'g')
grid on
box on
hold off

and producing essentially the same figure.

.

[Tahlea Perry]

Thank you so much! You are the best

[Star Strider]

As always, my pleasure!

I very much appreciate your compliment!