AsymptoticEquivalent
AsymptoticEquivalent[f, g, x -> x*] gives conditions for f(x) ~ g(x) as x -> x*.
AsymptoticEquivalent[f, g, {x1, ..., xn} -> {x1*, ..., xn*}] gives conditions for the multivariate case.
Examples
Test asymptotic equivalence:
AsymptoticEquivalent[x^2 + x, x^2, x -> Infinity]
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