To avoid the error, use element-wise multiplication (.*), because * is for matrix multiplication.
To plot multiple functions in a single plot, use hold on.
% Peter Daniel Bohlen
% Mech3080 hw2
% Part 2E
t = 0: 0.01:6;
x = (6 * exp(-0.5 * t)) .* cos((5 * pi * t) + (pi/4));
% ^^ element-wise
y = -1.5 * sin(5.5 * pi *t);
z = (6 * exp(-0.5*t)).* cos((5 * pi *t) + (pi/4)) - (1.5 * sin(5.5 * pi *t));
% ^^ element-wise
figure
hold on
plot (t,x)
plot(t,y)
plot(t,z)
grid on
xlabel 'Time (sec)'
ylabel 'Displacement (in)'
title 'Homework 2 Part 2E - Displacement vs. Time'
