,
,
,
,
or even expressions of those terms combined as if that would make them defined. I have made this post to answer these questions once and for all, and I politely ask everyone to link this post to threads that are talking about this issue.
,
isn't even rigorously defined in this expression. What exactly do we mean by 
.
,
does not exist in the first place, although you will see why in a calculus course. So the point is that 
?
indeterminate? In analysis (the theory behind calculus and beyond), limits involving an algebraic combination of functions in an independent variable may often be evaluated by replacing these functions by their limits. However, if the expression obtained after this substitution does not provide sufficient information to determine the original limit, then the expression is called an indeterminate form. For example, we could say that 
,
or ![\[0/0, \infty/\infty, \infty-\infty, \infty \times 0\]](http://latex.artofproblemsolving.com/2/6/0/260f97a1cf1ea8722ff97a29b83bac7bfe83e577.png)
etc etc. So what makes something undefined? In the broader scope, something being undefined refers to an expression which is not assigned an interpretation or a value. A function is said to be undefined for points outside its domain. For example, the function 
given by the mapping 
is undefined for 
.
is undefined because dividing by ![\[\overline{\mathbb{R}}=\mathbb{R}\cup \{-\infty,+\infty\}.\]](http://latex.artofproblemsolving.com/9/9/3/993c78b62ec2c84b5d77daa8e9a8cd6f70fcf904.png)
So instead of treating infinity as an idea, we define infinity (positively and negatively, mind you) as actual numbers in the reals. The advantage of doing this is for two reasons. The first is because we can turn this thing into a totally ordered set. Specifically, we can let 
for each 
which means that via this order topology each subset has an infimum and supremum and 
is therefore compact. While this is nice from an analytic standpoint, extending the reals in this way can allow for interesting arithmetic! In ![\begin{align*}
a + \infty = \infty + a & = \infty, & a & \neq -\infty \\
a - \infty = -\infty + a & = -\infty, & a & \neq \infty \\
a \cdot (\pm\infty) = \pm\infty \cdot a & = \pm\infty, & a & \in (0, +\infty] \\
a \cdot (\pm\infty) = \pm\infty \cdot a & = \mp\infty, & a & \in [-\infty, 0) \\
\frac{a}{\pm\infty} & = 0, & a & \in \mathbb{R} \\
\frac{\pm\infty}{a} & = \pm\infty, & a & \in (0, +\infty) \\
\frac{\pm\infty}{a} & = \mp\infty, & a & \in (-\infty, 0).
\end{align*}](http://latex.artofproblemsolving.com/6/d/8/6d8fc1eca5c791d430a7168cd3b37a02104fa318.png)
So addition, multiplication, and division are all defined nicely. However, notice that we have some indeterminate forms here which are also undefined,![\[\infty-\infty,\frac{\pm\infty}{\pm\infty},\frac{\pm\infty}{0},0\cdot \pm\infty.\]](http://latex.artofproblemsolving.com/a/0/b/a0b67076efcc014c78b2023be1151c84b57c1503.png)
So while we define certain things, we also left others undefined/indeterminate in the process! However, in the context of measure theory it is common to define 
as greenturtle3141 noted below. I encourage to reread what he wrote, it's great stuff! As you may notice, though, dividing by ![\[\mathbb{C}^*=\mathbb{C}\cup\{\tilde{\infty}\}\]](http://latex.artofproblemsolving.com/8/4/e/84ed3d6ab237df970333b87beaef5311caa46185.png)
which we call the Riemann Sphere (it actually forms a sphere, pretty cool right?). As a note, 
means complex infinity, since we are in the complex plane now. Here's the catch: division by ![\[\frac{z}{0}=\tilde{\infty},\frac{z}{\tilde{\infty}}=0.\]](http://latex.artofproblemsolving.com/1/6/0/160cb939707708ff4e0930724df2928af11d7fd1.png)
where 
and 
Furthermore, we actually have some nice properties with multiplication that we didn't have before. In 
it holds that![\[\tilde{\infty}\times \tilde{\infty}=\tilde{\infty}\]](http://latex.artofproblemsolving.com/8/e/0/8e035b4841d20c5ad671c46355cc667ca01e533b.png)
but 
and 
are left as undefined (unless there is an explicit need to change that somehow). One could define the projectively extended reals as we did with ![\[{\widehat {\mathbb {R} }}=\mathbb {R} \cup \{\infty \}.\]](http://latex.artofproblemsolving.com/c/0/4/c044ff37849acad3b8b280b9753539225a1276ca.png)
They behave in a similar way to the Riemann Sphere, with division by 
?
.
is rounded to the nearest integer and then divided by 
,
Y by
Hello AOPS community,
Should I take the Mathcounts/AMC8 Advanced course over the summer or the AMC 10 Intermediate course?
I'm a 7th grader who is aiming for DHR AMC 8 and AIME qual next year as well as nats mathcounts, but sillies a lot on some stuff.
Scores:
6th grade (2023-2024 year)
Mathcounts Chapter: 33 (21/12)
Mathcounts State: 19 (11/8)
AMC 8: 12 (idk how this happened)
didn't take AMC 10
7th grade (2024-2025 year, so right now)
Mathcounts Chapter: 28 (36 w/o sillies)
Mathcounts State: a score higher than my chapter score (I cant reveal exact until April)
AMC 8: 16 (the problems were randomized cuz online)
AMC 10A: 42 (guessed too much)
AMC 10B: 58.5 (:facepalm:)
In practice AMC 8's I consistently get around 20-22, and on mock AMC 10's I get around 9-12 problems correct (so about low-mid 80s). In mock state Mathcounts I get 26-28s. Several people in my state have said I have a free nats qual next year due to all the competition graduating, but I am aiming for 34+ on state next year for insurance and to see how far I can go. I also hope to get DHR AMC 8 in 2026 and AIME, but not sure whether to take the AMC 8 advanced or AMC 10 course. Should I retake AMC 8 advanced (i took it last summer) to get really good basics or take AMC 10 course, and will the AMC 10 course help me get DHR amc8?
Thank you for your help, its greatly appreciated
please respond I'm begging.
Should I take the Mathcounts/AMC8 Advanced course over the summer or the AMC 10 Intermediate course?
I'm a 7th grader who is aiming for DHR AMC 8 and AIME qual next year as well as nats mathcounts, but sillies a lot on some stuff.
Scores:
6th grade (2023-2024 year)
Mathcounts Chapter: 33 (21/12)
Mathcounts State: 19 (11/8)
AMC 8: 12 (idk how this happened)
didn't take AMC 10
7th grade (2024-2025 year, so right now)
Mathcounts Chapter: 28 (36 w/o sillies)
Mathcounts State: a score higher than my chapter score (I cant reveal exact until April)
AMC 8: 16 (the problems were randomized cuz online)
AMC 10A: 42 (guessed too much)
AMC 10B: 58.5 (:facepalm:)
In practice AMC 8's I consistently get around 20-22, and on mock AMC 10's I get around 9-12 problems correct (so about low-mid 80s). In mock state Mathcounts I get 26-28s. Several people in my state have said I have a free nats qual next year due to all the competition graduating, but I am aiming for 34+ on state next year for insurance and to see how far I can go. I also hope to get DHR AMC 8 in 2026 and AIME, but not sure whether to take the AMC 8 advanced or AMC 10 course. Should I retake AMC 8 advanced (i took it last summer) to get really good basics or take AMC 10 course, and will the AMC 10 course help me get DHR amc8?
Thank you for your help, its greatly appreciated
please respond I'm begging.
