chap 3

import numpy as np
import matplotlib.pyplot as plt
x=np.arange(-np.pi,np.pi,0.1)
y1=np.sin(x)
y2=2*np.sin(x)
y3=np.sin(3*x)

plt.plot(x,y1,x,y2,x,y3)
plt.xlabel("x")
plt.ylabel("y")
plt.show()