import numpy as np
import matplotlib.pyplot as plt


def f(x):
    return x**2 + 3

def g(x):
    return 3*x - 1


xa = np.linspace(-2, 3, 100)

plt.close('all')
plt.plot(xa, f(g(xa)), xa, g(f(xa)))
plt.legend(labels=('f(g(x))','g(f(x))'))

plt.savefig('plot_fun_plot_funfun.pdf')
plt.show()