Answer:
[tex]49x^2+126xy+81y^2[/tex]
Step-by-step explanation:
Use the square of a binomial theorem
[tex](a+b)^2[/tex]= [tex]a^2+2ab+b^2[/tex]
Now expand the given equation:
[tex](7x+9y)^2=49x^2+126xy+81y^2[/tex]
Hope this helps :)
Have a great day!
