import numpy as np

x_1 = np.array([1,15,-45,2,3,5])
y_2 = np.array([1,15,-45,7,31,65])

x_3 = np.array([])
y_3 = np.array([])

for i in range(len(y_2)):
  if y_2[i] > -20 and x_1[i] == y_2[i]:
    x_3 = np.append(x_3, x_1[i])
    y_3 = np.append(y_3, y_2[i])

print(x_3)
print(y_3)