uの値を変えるだけでしょ…
import numpy as np
import matplotlib.pyplot as plt
t = np.linspace(0,3,201)
us = np.sin(2*np.pi*t)
u = np.sin(2*np.pi*t)+np.sin(3*2*np.pi*t)/3+np.sin(5*2*np.pi*t)/5
# (1)
u =np.cos(2*np.pi*t)+np.cos(2*2*np.pi*t)+np.cos(3*2*np.pi*t)+np.cos(4*2*np.pi*t)
# (2)
u = np.sin(2*np.pi*t)-np.sin(2*2*np.pi*t)/2+np.sin(3*2*np.pi*t)/3-np.sin(4*2*np.pi*t)/4
plt.plot(t,us)
plt.plot(t,u)
plt.show()