(3a-7b)^2

Use (x-y)^2 = x^2 + y^2 - 2xy
Put x = 3a and y = 7b

Hey!

Let me help you!
My answer is
49*b^2-42*a*b+9*a^2
You can see how I got it here:
http://www.numberempire.com/fractionscalculator

Good luck

This is really fine than just giving the entire solution. Make the OP's solve their problem.