Question

If 3x-6y = 9z, which of the following expressions is equivalent to x^2-4xy+4y^2?

Answer 1

The first and the difficult thing is you need to tell that

x^2-4xy+4y^2 = ( x - 2y )^2

so from question you know 3x - 6y = x - 2y = 9z

finial : ( x - 2y )^2 = ( 9z )^2=81z^2

so the answer is D . Hope this would help you .