The square of a binomial in the form of (a + b)^2 is equal to (a^2 + 2ab + b^2). Similarly, for the given binomial, the squaring is done as shown below:
( 2x + 2/3y )^2
4x^2 + (4/3)xy + (4/3)xy + (4/9)y^2
4x^2 + (8/3)xy + (4/9)y^2
The final answer would be 4x^2 + (8/3)xy + (4/9)y^2.