We note that $361=19^2$ and $441=21^2$, so $x=21^2+2(21)(19)+19^2$. This is just the binomial expansion of $(21+19)^2=40^2=\boxed{1600}$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
$441+2(21)(19)+361=x$. Solve for $x$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
1600
$441+2(21)(19)+361=x$. Solve for $x$.
test