Need Help Solving Q. 16 Diag Sec In 12th ed Official Guide

[acrowson]

*Please refer to the answer solution in the OG (sets the context for my question)*

Specifically, I need help understanding why both sides of the equation in the second step expand differently from each other?!
In other words, how the heck do we deal with (Root 2X + 1)*^2?

[papgust]

It is just a simple formula, (a+b)^2 = a^2 + b^2 + 2ab

[root(2x)+1]^2 = (root(2x))^2 + 1^2 + 2*root(2x)*1

And from here, it gets simplified.