code: from mpl_toolkits.mplot3d import Axes3D
  import matplotlib.pyplot as plt
  import numpy as np
  
  x = np.arange(-3, 3, 0.25)
  y = np.arange(-3, 3, 0.25)
  X, Y = np.meshgrid(x, y)
  Z = 6*X*X + 4*X*Y + 3*Y*Y
  
  fig = plt.figure()
  ax = Axes3D(fig)
  ax.plot_wireframe(X,Y,Z) 
  
  xx = np.linspace(-3, 3, 100)
  yy = np.linspace(-3, 3, 100)
  zeros = np.zeros(100)
  
  plt.plot(xx,zeros)
  plt.plot(zeros,yy)
  
  plt.show()
  
apis: numpy.zeros matplotlib.pyplot.figure numpy.arange matplotlib.pyplot.show matplotlib.pyplot.plot numpy.meshgrid numpy.linspace