Solve the equation$\sqrt{b^2 + 2ax} = x+a$

Question

At an exercise I get the following equation: $$\sqrt{ b^{2} + 2ax} = x+a$$

My steps would be:
$b^2 + 2ax = x^2 + a^2$
so $b^2 + 2a - a^2 = x$

But this is completely wrong!

Answer 1

A common but serious mistake;

$$(a+b)^2 \neq a^2+b^2, \forall a,b \in \mathbb{R}$$