shouldn't infinity be included? So shouldn't the answer be [0,infinity]?
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No because ∞ isn't a member of the real numbers. No value of x yields ∞. Curved parenthesis is correct.
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If we could put a numeric value to infinity, you'd be right. But since we can only approach 'infinity', we can't close off the interval Think of the difference between (0, 1) and [0,1] -- in the second, 0 and 1 belong to the closed set, while they don't in the other, although we can get very close to 0 and 1 in the open set.
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No. That's the interval notation for infinity.. It's always written with one of these "( .. )" Never a bracket. It has something to do with the concept behind infinity that I don't know how to explain, but everywhere you go.. and every single time.. It will always be..
(-infinity .... or infinity)
Your book is right.
(-infinity .... or infinity)
Your book is right.
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Infinity is considered to be a concept, not an actual number. A line will approach infinity, but it will never actually touch infinity. Therefore, you use a parenthesis rather than a bracket. I hope that makes sense!