(2 1/3z + 1 1/2k)^2
= (7/3z + 3/2k)^2
= (7/3z + 3/2k)(7/3z + 3/2k)
= (49/9z^2 + 21/6zk + 21/6zk + 9/4k^2)
= 49/9z^2 + 7/3zk + 7/3zk + 9/4k^2
= 49/9z^2 + 14/3zk + 9/4k^2