Let's make a homework help thread!

Algebraically. You can find a limit by plugging in the value x approaches unless doing that results in a denominator of zero. When that occurs, there is a discontinuity. The discontinuity is removable if you can cancel out what makes the denominator zero. Hopefully you can find a source that can take your through the thorny details better than I can. My calc class is on the same topic.

(x-3)/(x+3)(x-3) has discontinuities at 3 and -3. The one at 3 is removable because you can cancel x-3 from the numerator and denominator.

Thanks. That clears up half of it. I have two questions about your answer. You say to plug in x for your limits. Does this mean plugging in x for the denominator or the whole thing?

Also, I'm a little confused on the "cancelling out" of the discontinuity thing. Is it factoring that cancels it out?

Plug it in for the denominator first, to see if it equals zero. If it doesn't, plug it in for the numerator as well and simplify. By the way, remember to write the limit statement (lim f(x) as x —> c) before the function until the step where you plug in the value of x.

If the denominator does become zero, factoring should be the first thing you try. Factoring itself is not cancelling, but breaking things up is the best way to see what you can cancel. In the example I gave, the denominator would most likely be given as (x^2)-9 on a test. When you factor that into (x+3)(x-3), you can see that one of the factors can be cancelled out with the numerator because they are the same.

If there are any square roots, you might need to multiply by conjugates.

edited 22nd Sep '13 11:24:46 AM by SnowyFoxes

A question is asking me to determine if y=3x-1 and y=-3x+12 are parallel, perpendicular, or neither. How would I go about doing this?

Check the slopes. If you have the slopes m1 and m2, and m2 = -1/m1, then you have a perpendicular line.

If m1=m2, then you may have parallel lines. I say "may", because you need to then check if they are actually the same line (i.e. you can convert one equation into the other).

If neither of these are the case, then the lines intersect, but are not perpendicular.

How would you express the arrangement of electrons using orbital notation? For example, it's asking me to do this for beryllium

You count the electrons in the atom. Conveniently this quantity equals the atomic number. Beryllium is 4.

Next you put the electrons into their subshells and shells.

Shell 1 holds 1 subshell, shell 2 holds 2, etc.

The subshells, in order, hold 2, 6, 10, and 14. and are named s, p, d, and f

Each subshell must be filled before one can be placed in the next. Same for shells.

Thus: Hydrogen is 1s1

Helium is 1s2

Lithium is 1s2,2s1 etc.

edited 13th Oct '13 5:09:58 PM by MrSparky

Need Excel help—I am trying to make a line chart such that years on deposit is the X axis, and annual percentage yield is the Y-axis, but it keeps treating the two sets of data as separate lines, and 1,2,3,4 as the Y axis.

So is beryllium 2 s^2?

Well, it's either 1s2 2s2, or if you want to use Noble Gas shorthand, it would be [He] 2s2.

Move to Boron, and the 2s shell is filled to capacity, so you go to the p shell; Boron is [He] 2s2 2p1

It goes (been years since high school chemistry; correct me if I'm wrong)

1s -> 2s -> 2p -> 3s -> 3p -> 4s -> 3d -> 4p -> 5s -> 4d -> 5p -> 6s -> 4f -> 5d -> 6p -> 7s -> 5f -> 6d -> 7p.

So far, no elements have been discovered which require going to the 8th orbital.

edited 13th Oct '13 7:21:09 PM by DriftingSkies

Technical question: how do you make the gridline in scatter graph of Excel 2013 square?

What are the formulas for:

• Na+ and Se(Superscript 2-)
• Fe(Superscript 3+) and Cl-
• Ca(Superscript 2+) and Se(Superscript 2-
• Ca(Superscript 2+) and N(Superscript 3-)

I'm assuming you mean to make them a neutral charge. You want the positive and negative charges to equal out. So if Fe is 3+ and Cl is 1-, then you need three Cl to counteract the Fe's 3+. There is one formula for you, and you should be able to figure out the rest.

So Iron(III) chloride?

Correct.

I need these answers badly for two assignments. I don't have much time until it needs to be turned in online, so please give me the answer here:

Question 1:Isotopes 46Ti, 48Ti, 50Ti. Abundances 77.300%, 14.300%, 8.400%. Masses 45.95263, 47.94795, 49.94479. What is the average atomic mass of titanium (on that planet)?

Question 2:Isotopes 180W, 182W, 183W, 184W, 186W. Isotopic masses 179.946706, 181.948206, 182.9502245, 183.9509326, 183.954362. Abundances 0.12, 26.50, 14.31, 30.64, 28.43.

Question 3:chlorine-35 chlorine 37. 75.8% of Cl atoms have 18 neutrons and 17 protons, the other 24.2% have 20 neutrons and 17 protons. Calculate average atomic mass of Cl, round to nearest whole number.

Question 4:98.89% of an element's atoms have an AM of 12.09 amu, other 1.11% have AM of 13.10 amu. Calculate AAM.

Question 5:Isotopes X, Y, Z. # of protons 14, 14, 14. # of neutrons 14, 15 16.. Abundance % 92.22, 4.69, 3.09.

Question 6:Isotope has has atomic mass of 63.48 amu, accounts for 69.15% Rest of element's atoms (30.85%) have atomic mass of 65.49 amu. Calculate.

This is do by 11:00 tonight.

Obviously this is past that deadline of yours, but I want to point something out. This is a help thread, not a demand the answers for your homework thread. If there's something someone is confused about that I can explain, then that's great. But to basically demand someone else do your homework leaves a bad taste in my mouth.

Mod Hat ON

Muse is absolutely right. You aren't going to get the answers here. You're going to get help with finding the answers.

Mod Hat OFF

GODDA Mit I'm not able to run this file in Visual Basic that I imported onto my computer and I don't know why. I don't have the option to debug it. I don't know of it has to do with how it's saved or what.

I'm a bit stumbled over this question;

Use the lengths of the sides of the rectangle below to determine the value of n.

l = 2n - 10, 1 = 18, and w = n - 4.

I know that the formula is A = lw, but I was curious as to how I should form the equation using these particular numbers. I don't have the perimeter, BUT I have to find the value of v.

edited 19th Dec '13 2:00:09 PM by fancywig

1 = 18? I assume that's a typo?

Hi, This isn't really homework but it is work that I need help with! I have a survey that I need answering for my dissertation, it's all explained on the survey. It takes a few minutes, 5 at most, and I'd very much appreciate anyone taking a bit of time to answer it. Thanks! http://www.surveymonkey.com/s/6NL5DLH

edited 28th Dec '13 10:29:46 AM by Alice_01

So, who here knows anything about the Russian language and is willing to help a bro out?

I'm taking some online courses and I've kind of been putting them off and the due date for it all is fast approaching and there are still some bits I don't understand.

Can anyone name a good source on the history of photography, especially the impact it had on society.

Um, guys. Need to finish 40 pages of DTP work in two days because the rest of the team is out of town. Anyone mind giving some motivational aid? Any tip on getting iStudio Publisher to play nice would be appreciated as well. Promise to answer whatever maths question I could after this. All my thanks!