isInfinite is:exact

True if the argument is an IEEE infinity or negative infinity
true if the argument is an IEEE infinity or negative infinity.
True if the representation of the argument is an IEEE infinity or negative infinity.
>>> isInfinite (_1 / _0)
True
>>> isInfinite (42 *~ micro farad)
False
Return true for both infinity and negativeInfinity, false for all other values.
isInfinite x returns True iff x is PosInf or NegInf.
Returns whether a given quotient is an infinity (+/-).