This is rather simple: Declare your t array, compute x(t) array, plot it with matplotlib.
import numpy as np
import matplotlib.pyplot as plt
# Declare t array
t = np.arange(0.0,2.0,0.01) # change your end point and step as you want it
# Compute x(t) with numpy
x = np.cos(2*np.pi*10*t) + np.cos(2*np.pi*25*t) + np.cos(2*np.pi*50*t) + np.cos(2*np.pi*100*t)
# Plot t with x
plt.plot(t,x)
plt.show()