Solution (source code)

= Solution

Multiply the <Maclaurin series> $e^{-x}=1-x+x^2/2+O(x^3)$ by the <binomial series> $(1+x)^{-1/2}=1-x/2+3x^2/8+O(x^3)$. The constant, linear and quadratic coefficients are therefore
$$
\boxed{e^{-x}(1+x)^{-1/2}=1-\frac32x+\frac{11}{8}x^2+O(x^3).}
$$