growing sinusoidal signal

import matplotlib.pyplot as plt
import matplotlilb.numpy as np

x = np.linspace(0,20,100)
y=np.exp(x/5) * 10
z=np.cos(x*2+10)
r =y*z

fig=plt.figure()
ax = fig.add_subplot(221)
ax.plot(x,y)
ax = fig.add_subplot(222)
ax.plot(x,z)
ax = fig.add_subplot(223)
ax.plot(x,r)
fig.show()