import numpy as np
from matplotlib import pyplot as plt

A = np.array([[5], [4]])
C = np.array([[4], [6]])
B = A.T.dot(C)
AA = np.linalg.inv(A.T.dot(A))
l = AA.dot(B)
P = A.dot(l)
x = np.linspace(-2, 2, 10)
x.shape = (1, 10)
xx = A.dot(x)
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(xx[0, :], xx[1, :])
ax.plot(A[0], A[1], 'ko')

ax.plot([C[0], P[0]], [C[1], P[1]], 'r-o')
ax.plot([0, C[0]], [0, C[1]], 'm-o')

ax.axvline(x=0, color='black')
ax.axhline(y=0, color='black')

margin = 0.1
ax.text(A[0] + margin, A[1] + margin, r"A", fontsize=20)
ax.text(C[0] + margin, C[1] + margin, r"C", fontsize=20)
ax.text(P[0] + margin, P[1] + margin, r"P", fontsize=20)
ax.text(0 + margin, 0 + margin, r"O", fontsize=20)
ax.text(0 + margin, 4 + margin, r"y", fontsize=20)
ax.text(4 + margin, 0 + margin, r"x", fontsize=20)
plt.xticks(np.arange(-2, 3))
plt.yticks(np.arange(-2, 3))

ax.axis('equal')
plt.show()