How to combine two functions in one graph?

How do I combine two functions in one graph and find the average value of that graph. The first function ranges from 0 to 85 degrees and the other one from 85 to 180 degrees.

Answer 1

[José-Luis]

 hold on

Answer 2

[Jan]

The more details you post, the less we have to invent.

x = 1:100;
y1 = rand(1, 100) * 85;
y2 = rand(1, 100) * 95 + 85;
plot(x, y1, x, y2);
% Or:
AxesH = axes('nextplot', 'add');
plot(AxesH, x, y1);
plot(AxesH, x, y2);

meanY = (y1 + y2) * 0.5;

Or perhaps "average value" means:

meanY = sum(y1 + y2) / (2 * length(x));