import numpy as np

A = np.array([3, 4])
B = np.array([1, 2])

A_plus_B = A + B
print("1. A + B =", A_plus_B)

two_A = 2 * A
print("2. 2 * A =", two_A)

norm_A = np.linalg.norm(A)
print("3. 向量 A 的长度 =", norm_A)

print("-" * 40)