7.调用numpy库实现矩阵的加、减、乘、数乘、方阵，求逆，求行列式， 已知A，B，C三个矩阵，编写代码，请将（1）-（4）结果输出到屏幕

好的，以下是你要的代码：

import numpy as np

# 定义矩阵A
A = np.array([[1, 2], [3, 4]])
# 定义矩阵B
B = np.array([[5, 6], [7, 8]])
# 定义矩阵C
C = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

# (1)矩阵加法
print("A + B = \n", A + B)

# (2)矩阵减法
print("A - B = \n", A - B)

# (3)矩阵乘法
print("A * B = \n", np.dot(A, B))

# (4)数乘
print("2 * A = \n", 2 * A)

# (5)方阵
D = np.array([[1, 2], [3, 4]])
print("D = \n", D)
print("D的逆矩阵 = \n", np.linalg.inv(D))
print("D的行列式 = ", np.linalg.det(D))

输出结果为：

A + B = 
 [[ 6  8]
 [10 12]]
A - B = 
 [[-4 -4]
 [-4 -4]]
A * B = 
 [[19 22]
 [43 50]]
2 * A = 
 [[2 4]
 [6 8]]
D = 
 [[1 2]
 [3 4]]
D的逆矩阵 = 
 [[-2.   1. ]
 [ 1.5 -0.5]]
D的行列式 =  -2.0000000000000004