import tensorflow as tf

# Create needed objects
sgd = tf.keras.optimizers.SGD(learning_rate=0.1, momentum=0.9)
var = tf.Variable(2.5)
cost = lambda: 2 + var ** 2

# Perform optimization
for _ in range(100):
    sgd.minimize(cost, var_list=[var])

# Extract results
print(">>>>", var.numpy())
# -0.007128528
print(">>>>", cost().numpy())
# 2.0000508