def test_arccos():
x = AD(0.5, 3, 'x')
z = x.arccos()
print('x=', x)
print(z)
assert z.val == [np.arccos(0.5)]
# np.testing.assert_array_equal(z.der, np.array([-3/np.sqrt(1 - 0.5**2)]))
assert z.der == [-3 * (1 - 0.5**2)**(-0.5)]
def test_arccos_p1():
x = AD(1.1, 3, 'x')
with pytest.raises(ValueError):
x.arccos()