If
\[
\lim_{x\to\infty}\left(1+\frac{a}{x}+\frac{b}{x^2}\right)^{2x}=e^2,
\]
then \(a=\)
Show Hint
For limits of the form \(\left(1+\frac{f(x)}{x}\right)^{cx}\), only the coefficient of \(\frac1x\) contributes to the exponent of \(e\). Higher-order terms such as \(\frac1{x^2}\) vanish as \(x\to\infty\).