Respuesta :

(3x+7y)²  the form is  ax² + 2ab + b² where a is 3x and B is 7y

so its

(3x)² + 1(3x)(7y) + (7y)²

9x² + 21xy + 49y²


Answer:

9x^2 − 42xy + 49y^2

Step-by-step explanation: